I have several transactions that are in the wrong category. how do I delete them?

is there a way to see transactions under each category? I do not know which transactions are incorrect by looking at the receipt list

Unfortunately Loyverse does not allow to change receipts. It is done for security reason to prevent possible manipulations.
It is difficult to understand the meaning of the category in connection to the receipts. You may mean that you chose wrong payment type(cash or card) for receipt. In any case it is impossible to correct the receipt to change payment type. The best way to solve this  is to make refund of that receipt and make a new sale with correct payment type.

https://help.loyverse.com/help/how-issue-refund-loyverse-pos

Could you please, clarify the meaning of transaction? Do you want to sort receipts by items category? But in the same receipts there may be items from many categories.