How to Replace keyboard

Depends on the generation. G6 and under are modular but the G7 and later models build it into the palmtest where you replace both :-(. That said it isn't hard to find them but they can be pricey. What you can often do is find good used ones with no wear on them due to issues like persistent MDM bricking motherboards so they usually end up being ~$50-60 for good low use upper cases.

Take the model and search on eBay for a palmrest assembly if it's a G7 or newer, or if it's the G6 and older the keyboard has a sticker on the back. That's your reference.