I bought credit to my apple id mistakenly using my apple wallet. How do I refund this amount?

Normally, you can't transfer the account credit back to your payment method. If you still want to try, contact iTunes Support for assistance. See the Apple Support articles below for contact information.   

iTunes Support – world wide   -

Apple Support schedule phone call     -

Billings and Subscriptions   -

If necessary, try Twitter

https://twitter.com/AppleSupport.   -