I have created a form in one account (as author) which I can share with others (as co-authors) but how can I remove it from the original account without deleting it - i.e. I want the co-authors ro remain authors! or nominate one co-author as author? Is this possible please?
It's not possible to transfer ownership of a form. The only way to effectively transfer ownership is to have a co-author duplicate the form in their dashboard, and start working with that new form. Please refer to the following document, specifically the "Share the Form File and Duplicate" section.