This will help you. In my case i broken my space key i was unable to fix it. Then after some research i found this article first i visited service centre to buy a new key but in my local they say they don’t have because my mac is too old. Then i visited local repainting shop and ask for a key what the shopkeeper did is he remove a key from a old not working laptop and replace it to my laptop.
While replacing the key please watch 10 - 15 video online it will help you. Replacing keys of butterfly keyboard is really complex.
All thanks this article just because of it i saved my money else i have to buy a new keyboard.