How do I / can I delete or transfer an alias?

I created an email alias for my child using her name. I just got her an Apple Watch, and we want to use this address as her child account. Process won’t let me, so I want to delete the alias so we can reassign the name to her.

I know Apple may not allow this.

How do I get this email address with my child’s name to her, assigned to her Apple Watch?