Can I reverse an already confirmed transaction?

Decentralized blockchains are immutable, meaning the data they contain cannot be changed. When the transaction is confirmed and shows as successful, there is nothing we can do to revert/cancel it. Usually, when the transaction is confirmed, it's final, and is added to the next block.

You can only cancel a transaction while it is still pending.

We cannot revert a transaction that is already completed.

What you can do is to check with the receiver or receiving app to see if they could do anything on their side (i.e. return your funds via a new transaction).

For more on transactions in general, see here.

For instructions as to how to cancel or speed up a pending transaction, see here.