If you want to return your tablet to the supplier, you have to sign it out in the personal user account.
If the tablet is not signed out, it cannot be used any further for security reasons.
A more detailed description of how to sign out from a Google user account you will find below:
- Open your Google account
- Choose the option “Security” in the navigation area on the left.
- Choose under “Your devices” the Galaxy tablet
- Choose the corresponding device and click on Sign out
- Confirm with Sign out
- Finish the process with “OK”
The tablet now shouldn’t appear anymore under "Your devices”.