Try tapping on the keys a few times before you replace it, keyboard repair 101
My advice if you are not great at soldering would be don't do it , you want to be good at anything your going to do, get someone who is great at it to do it, and you do the things you are good at
Unless you don't mind breaking it, at $5 it could be good practice
Those Atari keyboards have little rubber buttons under the keys don't they? And don't these fail?