how can i cancel my apple care?

See here: How to manage your AppleCare plan - Apple Support

If you pay for your AppleCare plan on a monthly basis, you can manage or cancel the plan from your iOS device, Mac, or PC. Learn how to cancel your subscription.

View, change or cancel your subscriptions - Apple Support.

Note that AppleCare is not a subscription but a full product purchase. There is nothing to cancel.