Login to stripe, click customers > search for the customer by name or email address.
Select the member that you need to refund.
From the action menu, select the refund payment option.
From here, you can determine the refund amount, select a reason, and click refund.
Refunds are processed immediately by Stripe but can take 5-10 business days to appear in the customer's account.
Note: If you're using a payment system that is not the internal MemberUp checkout or stripe, please refer to the documentation of the payment system you're using to learn how to refund using that.