Hello Victoria84, you can raise a VAT only transaction for this, here are the steps to follow below or you can look on this help article.
1. If it's related to Sales, you can create a Sales receipt transaction.
2. On the first line of the transaction, select the category and enter the VAT amount with 20% VAT. If it's for Purchases, create an Expense transaction.
3. On the second line of the transaction, select the same category and enter a negative VAT amount with No VAT code.
4. Below the subtotal, change the VAT amount to the total VAT amount you want to record in the VAT return.
5. Lastly, click on Save and Close.
VAT only