If you have multiple athlete profiles that want to be linked to the same billing (unlike subaccounts, where you use one email), here's how to do that:
Why not just add as a sub account?
-Because sub accounts use only 1 email for access. This circumstance might be for a husband and wife or a parent with a older child (teenager) that wants to manage their own account with their own email, but parents still want to pay for the membership.
You first have to cancel any memberships associated with the account you want to change (Do NOT change anything to the person's account you are using for the billing)
Then, go to the athlete's profile that you are changing and under 'Member Info' you'll find 'Billing Information'
"Stripe customer id cannot be changed while member has active membership"
This is why you cancelled the membership in step 1
When you cancel the membership, you'll be able to click checkbox 'Link Billing to Another Member'. You'll be able to search for the member you want to be the primary billing account.
Restore the membership to that profile. You can offer 'Free Trial' until the next billing date if you cancelled the membership early before the next billing cycle.