You can add specific account codes from Xero against the matching Unit type or Insurance. This will export in the invoices export formatted for Xero.

Edit the unit type you would like to assign a code. Enter the code in the section Xero account code and hit Update unit type to save the changes.

Edit the insurance level you would like to assign a code. Enter the code in the section Xero account code and hit Update cover level to save the changes.