childs iwatch esim has linked to her phone, how do I reverse this?

My child’s watch (logged in with her Apple ID managed through family sharing) has an eSIM. The number for the eSIM has somehow attached to an iphone that she uses which is also logged in with her Apple ID. When I go to remove the phone number from the phone it is telling me I have to deregister the number in order to remove it from the devise. Is there anyway around this?