Default email for calendar service

Hi there, 
My hotmail address (which is also the address under which my zoom account is registered) used to be my default address for sending out calendar invites. 

I changed it to another gmail address recently and want to change it back to my hotmail address.

Zoom indicates that I can change the calendar by going to the Schedule Privileges but this doesn't work as it is only intended if other people are supposed to be enabled to send invites on your behalf. 

Otherwise, in the calendar settings, I wanted to add a new calendar and that should have enabled me to switch to the original hotmail address for calendar invitations. The issue is that when I tried to register my hotmail address, I get an error message indicating that I cannot register personal email addresses. 

Can anyone help? 

Many thanks. 

Themba