Child in Family has primary and non-primary email addresses. I need to swap the primary! How???

My child was initially setup with an icloud address using email #1

Later, we added email #2 but #1 is still the primary.

How can I make #2 the primary? I don't see an option to "change" the primary when I login via appleid.apple.com -> security -> email and phone numbers

Thanks to help me out on this :)