Welcome to the thread, @bl11. Let me get the help you need about your Master Admin concern.

In QuickBooks Online (QBO), it could only have one Master Admin. If you'd want to change the Master Admin role, you must be signed up as the Master Admin to transfer it. 

Moreover, to change the role, the user must be listed as an Admin first. If they’re not, you can choose the Edit ✏ to change them to an admin.

Once done, when you select the small arrow in the Action column, you now have the option for Make master admin.

For more information about this process, you can read this article: Change your QuickBooks Online master admin user. 

Touch base with me if you need a hand with any QBO related concerns. I'm always here for you. Have a great day!