The D key just fell off my keyboard. I can use D but have to carefully press the little knob. The key cover (?) is completely off. How do I replace it? I tried pressing down on the key cover in the hole it left. That didn't work. No Apple store within 100 miles, so can't take it in. Please help.
It's a very delicate process but once you figure it out, it's very easy afterwards. Tweezers also comes in handy too.
Did the two latch pieces come off with the key? You will have to take them off and put them back on first. Hopefully the little tabs didn't break which keeps them attached to the keyboard.
To see how how they go back on is easier visually then describing so remove any key next to it by taking the tweezers and prying just the key from the top. That way you will leave the 2 pieces underneath in tact. Once you get those attached, just center the key up and press down until it snaps.
If the keycap is broken you'll need to order a replacement. ifixit.com and others sell them. The following link explains how to assemble the scissors and install the keycap.