Hi! I understand your friend is looking to delete his account and he can definitely contact general Customer Support, which Tiami provided. However, your friend c*so try to get his account back, which he can through this link: Click Here

Your friend will be asked questions by the support team to authenticate his identity as the Owner of the account. However, it might be a better solution than deleting the account.

~Jib

Additional note: I know you guys are aware that sharing account does break the Terms of Service so getting the account back is not guaranteed, but it's worth a try.