How do I cancel an accidental annual subscription and get a refund on Apple Account?

If you need to request a refund, instructions are provided at the links below,

If you want to cancel a subscription from Apple - Apple Support

Request a refund for apps or content that you bought from Apple - Apple Support

If additional assistance is required from Apple Support, please use the links below to contact Apple Support. If you’re in the US please call  1-800-MY-APPLE or outside the US, consult the support articles below.

Contact Apple for support and service - Apple Support

Live Chat with an Apple Advisor in Messages. 

Live Chat not available in all countries and regions. 

Accidentally? That requires double clicking the side button with the amount showing on the screen, followed by authorization with FaceID/Passcode. Not something that can be done accidentally. If you started a free trial, you would have seen the expiration date of the trail and the subscription price, with the message that to avoid the subscription charge, you need to cancel the trial at least 24 hours before it expires.

For that reason, most transactions in the App Store are final, but at times, Apple may provide a compassionate refund. It should never be expected though, and all you can do is try.

Request a refund for apps or content that you bought from Apple - Apple Support

To cancel a subscription:

View or cancel app subscriptions on iPhone - Apple Support