How can I fix my keyboard if some keys don't work

In short, you can’t. You’ll need a new spare part, called a top cover. The keyboard is integrated into the plastic cover that also houses the touchpad.

This is not a CRU or customer replaceable part. A certified engineer has to replace it, as basically your whole laptop has to be transferred over to the new top cover, including your motherboard. You basically have to disassemble the entire unit, apart from the LCD assembly.

If the unit is still under warranty, call HP support. As long as they don’t think the keys stopped working due to CID (customer induced damage), you’ll get a new part and a HP CE will perform the repair.

If you don’t have warranty, you can still order the part and replace it yourself, but you also risk damaging your hardware. Lots of delicate connectors and components. Still, if you can find the hardware maintenance manual for your laptop and get the part, proceed with caution and slowly disassemble the unit and the reassemble it. This takes me about 30 minutes at the most. It might seem difficult, but anything that has been assembled can also be disassembled and put back together again. There’s actually instructions on the motherboard where every screw goes, if you look closely. Take a photo of the unit before you disassemble it and use that as reference.

Read up on ESD protection and damage before attempting repairs on any hardware. Take the necessary precautions and use the correct tools. Everything tool need can be bought on ifixt by the way. I use many of them on a daily basis.