Assigning admin access to specific locations is accomplished by assigning a franchise group to the admin user account and in certain situations, an admin may need access to a location outside of the Franchise.
When an admin is assigned to a franchise group a location outside of the franchise can NOT be assigned to the admin. In this scenario, the location outside of the franchise would have to be assigned to the franchise group for the admin to have access to the location.
If you'd like this ability in the platform, reach out to your CSM to submit Product Feedback to inquire if this ability can be added to the development roadmap.