How to change acount customer mail and VAT?

Some body know how to change acount customer mail and VAT?

I bought a theme by creating an account separate from mine to send it to my end customer who will update and maintain is website.
I need to put his personal email in the SETTING of “personal-information” and VAT without succes…
(the system keeps my contact details).

Does anyone have the solution?
Thank you for all.

You won’t be able to amended tax info - this will only ever be affiliated with the details used at the time of purchase

OK, do you know a solution to use the Envatomarket extension only with this theme?
When I install the extension in the WordPress theme, it appears with my others themes already purchased.
I don’t want the customer could buy something with my credentials.
Thank you for help.