I would suggest openig a support ticket:
https://support.chess.com/customer/portal/emails/new
Explain the situation there. I would assume the would require some verification that account was supposed to be yours. Another option would be to have the family member that gave the accout to open a ticket explaining the situation. But the staff member that gets the ticket would be able to provide the best information.
Hi, I asked for a platinum membership for a gift this Christmas, and my family got it for me, but didn't ask for my account information and just created one and bought the membership for it. I would really like to continue to use this account, and not the one that now has the membership. Is there anyway to transfer the membership to this one and delete the old account? Thank you.