My letter 'i' key completely stopped working yesterday.  And for awhile I've been having 'intermittent deadness' w/the right arrow key as well.  When I found how easy it was to fix the 'i' key, I pulled the right arrow off and cleaned that too.  In a nutshell... a 'lil DeoxIT on a lint-free patch... clean the circle where the cup presses down.  Dry it off...  Voila'.  (Rubbing alcohol would probably work too.) 

But...FIRST THINGS FIRST!!  If you notice one of your keys is dead while working on your Macbook Pro, IMMEDIATELY go to your System Preferences and REMOVE THE PASSWORDS from your accounts. (leave the field blank when asked for your NEW password.)  I also tried changing the Privacy setting where the box is ticked "Require password after screen saver and sleep" but that's glitchy and it didn't allow it.  Changing my password to blank was especially important for me because my user account (my main working account) has 'i' in the password.  Thankfully my Admin account does not have an i, but if both accounts had 'i's in the passwords and the screen locked, I would have been locked out until I fixed the darn key.  Then the next thing I did was a Time Machine backup, just in case the little Macbook was a gonner.  I had to launch a text file and copy the letter 'i' into my clipboard, because I was not able to make changes to Sys Prefs without typing in my current password.  But to be safe I also nixed the password in my Admin account, because if one key stops working, who's to say how long it's gonna be before some other ugliness raised its ugly head?

Basically w/these 2013 Macbook keys (same design as IBM tablets circa 2012-2015, it's a scissor scaffold) you simply pry the actual key off, slowly and carefully starting with a corner.  When the key is off you then pry up and remove the 'scissor lift', and the cup.   I like spudging (prying with a plastic tool, or fingernail) the top, or bottom, of the key first, and then the opposite side. The little hinges underneath the keys are paired, two top, two bottom.  So for me it makes sense to try to release them in pairs. 

PAY ATTENTION to what the parts look like and lay them on your worktable exactly how they come out.  The capital letter 'i' key is symmetrical, so it's kind of easy to try putting it back in wrong.  The underside of the keys are NOT symmetrical.  Neither is the scissor hinge.  So get it right.

When I pull a letter key off, I put my finger on the edge of the key opposite the side I'm  prying. I try to minimize the stress on the plastic parts by just applying force where I want it while holding the other side in place.  Maybe I'm overthinking it.  But I was able to take two keys off, and put them back, with no breakage.

Now the scissor scaffold part, the top two snaps (top meaning the top of the letter or number if you are reading it) you can pry up and snap free.  But the bottom, don't just try to rip that up - you will want to stand the scaffold straight up first.  Once the top two snaps are loose (closest to the screen), pivot the little part upwards on its back two hinge pins.  Once the scaffold is pointing toward the sky, it comes out very easily from its two bottom hinges.  Put it back the same way.  If you're lucky enough to get the key off without disturbing the scissor, then simply remove the cup and clean the gold pad under the cup with Deoxit.  I used a gun patch wrapped around a plastic tine from a disposable fork, with DeoxIT to restore and clean the functionality of that little pad under the cup.  The gold pad wasn't really all that visibly dirty, but cleaning it made all the difference.  I rubbed it a few times, then dried it.

One difference I noticed:  The normal size keys have a circle in the middle of the scissor hinge that's more than big enough to accommodate the cup.  The cup just sits right in the middle.  But the smaller RIGHT ARROW key I cleaned has a much smaller circular opening in the scaffold, and I had to pop the lips of the cup underneath the scissor before putting the key back on.

The brilliant thing about this 'back inna day' scissor keyboard design is, everything is press-fit.  They come out by spudging up - go back by pressing.  Think of one of those plastic folding tables where you tuck the legs up and snap them in place for storage.  Basically the same. A cheap white plastic diner fork helps, along w/fingernails.  If your key is damaged, try finding your part here: https://www.replacementlaptopkeys.com/

I found some hair and some stains under the keys... after all, this is a 2013 machine and I'm the 2nd owner.

If the plastic scissor comes apart, which does happen often during removal of the key (usually the inside detaches from the outside @ one of its inner pin hinges), you have to very gingerly insert that back together before reinstalling.  The inner scissor hinges will not simply go back together by laying it flat and applying pressure.  You have to delicately FLEX/PULL the outer portion wider to make just enough room for the tiny plastic pin to slip back in.  Once again, take care when laying these parts aside to keep them in the same orientation as they were when you pulled 'em out - or thatz just another stupid puzzle.  I needed a magnifying glass to even see what the ****'s going on in there.
I haven't done a key repair on a laptop since about 2015, so I was rusty.