If a transaction is in the wrong category, it's easy to re-categorise!
There's two ways to re-categorise a transaction. The first is to tap on the transaction, then tap the box which displays the current category and you'll then be shown which category you'd like to place the transaction into. The second method is to swipe left on a transaction and you can then tap 're-categorise'.
Once you've selected a new category, Snoop will then prompt you if you want it to re-categorise all past and future transactions to this merchant in the new category you've selected.