It's not possible to change the manager of a Premium Family plan, but if you know the account credential of the current manager, you can cancel. Then, when all accounts go back to the free service at the next billing date, a new manager can start a new Family plan.
If it's not possible to access the account page to cancel the Premium Family subscription, I'd recommend reaching out to the Customer Support for further advice. You can find the contact form here.
I hope it helps!
Emilia_8Rock Star 5
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