You want to refund a transaction made on your platform?
If the transaction was completed within the last 60 days, you can make the refund on your own. See this article: Refund a transaction
If the transaction is older than 60 days, you need to contact the WePay team so they can refund the donation. Here is the link to contact WePay’s Technical Support directly: https://support.wepay.com/hc/en-us/requests/new