How to renew a domain name associated with Apple?

Hello,

Apple does not manage domains in any way shape or form.

If you set up your email domain to be used with iCloud email, your domain registation, management and renewal has not changed from its original registrar, and as such any renewal of the domain name, payments and other management should still need to ocurr thorugh whatever domain registrar holds your domain name.

If you purchased a domain through an Apple device's Settings, then the domain is managed by Cloudflare and you would need to log in to Cloudflare with the account created during the domain purchase with them to pay and manage your domain.