We often have mindset that once a gmail account is set-up in a smartphone, then it can't be deleted or rolled back. Now the MIUI 8 and MIUI 8.5 doesn't offer several features as well, but if you are stuck in that situation, I prefer and advise you to watch this article because I'm demonstating here how to delete a synchronized Gmail account from your Xiaomi Redmi device:
Open and Go to Settings
Go to General Settings.
Tap Google in the Account section
Now select the Gmail account which you want to delete (in case there are multiple Gmail accounts)
5. Open the sync screen and tap the Menu button
6. Tap on Delete account
Your account is successfully deleted now. Don't just add your Gmail accounts as now can even delete or remove them