Hi Siwi_tpwk,
Greetings!
Thank you for posting in Microsoft Community.
I'm sorry to hear that the keyboard stopped working after being exposed to a liquid.
You may try to boot the device to the UEFI settings to get verifications. UEFI environment is outside the Windows system so any issues that persists on the UEFI could be potential hardware issues. Go to settings > Update & Security > Under Advanced Start up , click on Restart Now, once you're on the UEFI settings, Go to Troubleshoot > Advanced options > Click on Command Prompt > Type "notepad" > test the keyboard.
If it's confirmed that it's not working on the UEFI settings, then we can say that it's already a hardware issue on the type cover keyboard and the only option for this is an exchange to a replacement keyboard.