Open the Gmail app or go to Gmail in a browser
Tap or click your profile picture in the top right
Select Manage accounts on this device or Google Account
Choose the account you want to remove
Tap or click Remove account
Confirm the removal
On a browser, sign out of the account if needed
To remove Gmail from a device, remove the Google account from the device settings
To remove an account from the Gmail app, repeat the steps for each account you want to delete