The thing is very simple if you want remove Gmail account from your Android smartphone. 1. First thing go to Gmail app and tap on your account icon on top right corner.
2. Now Tap on “Manage Other Accounts on this device”
3. Select Google and Select account that you want to remove.
4. After Selecting your desired account tap on “More” like shown in the picture below.
5. Finally, Tap on Remove Account and you are done. Gmail account is removed from your smartphone.