If tax was calculated for an invoice, you are not able to adjust the customer details. Since tax is calculated at the time the invoice is paid the customer’s address and tax ID/VAT information is locked at this point in time.

You can determine if tax was calculated for an invoice if there is a “Tax” column on the invoice:

If tax was not calculated for an invoice, you can update the customer details. This can be done by editing the customer record from the admin panel or having your customer edit their own details from the customer dashboard.