Admin create service record question

Problem: An admin from Admin Portal uses the new button to create a service record. It automatically assigns the service record to them and does not change when the admin group is changed to a group they are not in. How can I make it change the assign to to none if the admin group is changed? or Make it so the admin can only create new service request for the templates assigned to their group from the new button in the admin portal but be able to create any service records from the self-service portal. Thank you for your help.