Main Account owner has left organisation and Account details need to be changed to replacement employee

Main Account owner has left organisation and Account details need to be changed to replacement employee

We have a situation where the staff member that set up our Zoho Account has left the organisation. I am trying to change the user settings to reflect the details of the new employee taking their place.

I can change the username and various other details but not the email address.

Can anyone advise how to do this please. Ideally I want the entire account left as it is, only changing the username, user contact details and email address.