When Offboarding a client, the best practice to remove Thirdwall protection would be to open the Location screen of the client you are offboarding and "UNDO" all effective Thirdwall policies.

This can be done by clicking the "UNDO All Policies" icon in the lower left-hand corner of the Thirdwall Location screen and following the prompts.

This will remove all active Thirdwall policies from the Location.