If you see a duplicate charge from a merchant (and they have confirmed they only charged you once) likely what will happen here is one of the authorizations will expire* in 7-10 days, while the other is settled and collected by the merchant.
You can check the authorized/settled status of a transaction in-app by selecting on the specific transaction in your Activity Feed.
As long as the transaction is in an "authorized" state on your app, there is a chance that the charge will expire and return to your account.
If you see both transactions labeled as "settled" within your app, then reach out to us in-app to investigate this further.
*Unfortunately we do not have the ability to expedite the second authorization's expiry. Please wait the 7-10 days timeframe for the funds to return.