There are a few different ways to remove a Google account from your Amazon Fire HD 8, depending on whether or not you have access to the device.
If you have the device:
- Go to Settings > Accounts > Google and tap on the account you want to remove.
- In the top right, tap More > Remove account.
If you don't have the device:
- Go to the Google Account security page.
- Under "Signing in to Google," select Two-step Verification.
- Under "Backup codes," select Delete.
- Enter your password, then select Delete.