Hey Supama_5
You can do this using the Supplier Credit - to create to represent the refund being agreed. You'd reference any VAT and Expense accounts used for the original purchase on this Supplier Credit.
You can then create a Deposit to Creditors, - selecting the Supplier for the creditors to affect. This is to represent the money being placed back in your account.
Using the Pay Bills screen, or sometimes the Cheque screen, select the deposit and supplier credit and link the two together.
We've included a handy how to guide here with more in depth detail. Any questions at all on this please let us know, we'd be happy to help further.