In Frisbii, you can add, edit, deactivate or delete VAT rate values.
To do this, you must make these changes in multiple Picklists.
The Frisbii objects "Invoice line item", "Subscription line item" and "Quotation line item" have their own Picklists.
A global Picklist centralizes the VAT rate values for the "Corporate name", "Account", "Product", "Accounting data" and "Product rule" objects.
Edit Picklists on Frisbii objects
Steps
1. Go to the Object Manager in the Setup (or, for the Classic interface, to Setup > Elaborate > Create > Objects).
2. Select the desired Frisbii object.

3. In the fields, find the "VAT (%)" field and click on it to modify its values in the associated "Values" list.
For more information on the maintenance of selection lists, we recommend the module Managing your picklist values.
Edit the global Picklist
Steps
1. Go to Objects and fields > Picklist value sets in the Setup (or, for the Classic interface, to Setup > Design > Create > Selection list value sets).
2. Select the value set "VAT rate" in order to edit its values in the associated list "Values".

For more information on maintaining global pick lists, we recommend the Value sharing through global value sets on Salesforce Trailhead.
To select a VAT rate and to know the automatic initialization rules please consult the article : VAT rate selection and automatic initialization rules.