How to change a broken key?

I did not find any instruction how to repair a key an the keyboard. In older models (G6, G5 ...) the keyboard was exchangeable. How can a change a broken key?

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crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 0
crwdns2934285:0crwdne2934285:0