To add a VAT: 

1. Click on the Store Management tab on the top tab fields then Tax Rules

 

2. If you don’t have an existing Tax Rule, click on New or Create a new Tax Rule. If there’s an existing rule, double-click on this specific Tax Rule. 

 

3. Once, the tax rule section open, please make sure you pick the VAT field in order to perform the change. Make sure you press Save to retain the changes