How do I correct the buyer on an issued invoice?

An issued invoice cannot be edited. Re-issue it instead:

1. Open the order and select More > Documents > Re-issue invoice….
2. Check the Customer or company name, Street address, Postal code, City, Country, and tax number, and correct what is wrong. Fields left blank on the original invoice are filled from the customer or company record as it reads now.
3. Enter a Reason (printed on the credit note), for example "Buyer details corrected".
4. Select Issue credit note and new invoice.

Tiquo issues a credit note that cancels the original invoice in full, then a new invoice to the corrected buyer. Both take the next numbers of their series and cannot be undone. No payment is refunded, and the original invoice stays in the order's records as cancelled. A later refund on the order credits the new invoice.

You need the Create & manage orders permission. See Re-issue an invoice.