Good to have you here, dusan.
The refund category in QuickBooks Self-Employed (QBSE) is unavailable. If this a downloaded transaction, you can exclude it on the Banking page.
If you need to record it QBSE, it would be best to consult your accountant on how what specific category you'll need to use. They'll also help you on how to handle them into your account.
If they will give you instructions that you find challenging to enter it in your account, we will help with it.
To learn more about categorizing transactions, please refer to this article: Categories in QuickBooks Self-Employed.
I'm just one click away if you need a hand with preparing your year-end report or any QBSE related. I'm always here to help.