Hello @Karen Garland !
Welcome to Microsoft QnA!
I have been recently in a similar case
If you select Subscriptions from Azure Portal and then your Subscription
Go to Properties and you will see the Change Service Admin
If it is greyed out ,,,,
The only way to do that is by Hep & Support
Open a new ticket and the Support Engineers will guide you to do that
Make sure to describe precisely the issue
I hope this helps!
Kindly mark the answer as Accepted and Upvote in case it helped!
Regards