Hello. Perhaps I agree with the user above. If your keyboard has already fallen into disrepair, it is simply pointless to try to fix it, unless of course, we are talking about a keyboard on a laptop.
It is much easier to buy yourself a new keyboard and I would like to advise you to also buy yourself a silicone keyboard skin as with this cover your keyboard will last much longer. Personally, I buy such covers on the website https://neconnected.co.uk/what-is-the-point-of-keyboard-covers/ . One of the best manufacturers in my opinion. I advise you to try!