I need to request a refund for an accidental subscription

You have to cancel that accidental subscription & the request refund.

See this Apple article: See your purchase history for the App Store, iTunes Store, and more

https://support.apple.com/en-us/HT204088

Look here, you can

• View your purchase history

• Cancel a subscription

• Request a refund

• Verify unfamiliar charges

• Add or remove a payment method

https://support.apple.com/billing