Depending on your success in searching to find the replacement key-caps and tiny parts that reside
beneath them in the 12-inch MacBook (2015+) and if you can get the exact ones you'd need, that is
a likely avenue to explore to attempt to resolve this issue. And also use compressed or canned air
to clear dust. Some brands of keyboard/screen protectors that stay in place in use, help keep keys
from getting stuff underneath.
You'd likely need to do more than this if the keys need major cleaning underneath..
How to clean the keyboard of your MacBook or MacBook Pro - Apple Support
Due to several Mac browsers between several different Mac OS X, relevant bookmarks to locate the
key-cap replacement sites and how-to take them out/put them back, are harder to find...
So here's an search result that yields some; others may include repair companies who offer parts
and have a page online with images. Each key may have up to three parts you could replace.
https://duckduckgo.com/?q=how+to+replace+keys+in+macbook+12-inch&t=ffsb&ia=videos
In any event...
Good luck & happy trails! 🙂