Reactivate original account after legacy contact activation

We inadvertently activated a legacy contact that we didn't intend to activate. How do we reactivate the original account?

Longer version: I've been managing my late sister's Apple account while administering her estate. A couple of her Apple devices, including a watch, were given to our cousin (who was one of my sister's legacy contacts). That cousin was having trouble getting the watch associated with her account and set it aside while dealing with other issues. Recently another family member offered to get it working for her, and used her legacy contact code.

I got the email notification of this (to my sister's Apple address) and sent the cousin an email asking what was up, but never got a response (I learned today she never got the email). Life happened so I never followed up and never hit the "delete this request" link, and today got the notification that the account had been transferred and I no longer had access.

I contacted the cousin again today (using a different email address) and she called me and explained the mistake.

So now we need to know what we need to do to give me access to the account again. The cousin hasn't yet set a new password and 2FA.

Thanks.