Changing invoice details is allowed only once and only in the same month the payment was made. To edit your invoice, log in to your dashboard and click on "Account Details" below your profile card. Select "Contact & Billing" to update your billing details which will reflect on your invoice, if it's done for the first time and in the same month.
Please note that GST number can be updated only on Indian payments and not on Export invoices. If you wish to display a VAT/Tax number on your Export invoice, you can add the same next to your company name, for example, "TransTech Restaurants LLC (VAT: 987654321)"