Primary & Secondary email addresses mixed up

My family have been with Cable London/Telewest/Virgin Media since the early 2000’s.

When I did the initial computer setup, I put myself as the main account holder, with my partner as the secondary account. These were both setup with @blueyonder.co.uk email addresses.

We unfortunately had a computer virus about 15 years ago, and while re-installing our information I mistakenly switched around my partner and I’s accounts while re-setting up. This resulted in her being seen by VM as the main account holder, with me as the secondary account holder.

This has not been a major problem since - until recently. As we now have to sign in to our emails with our VM identities, I am receiving my partner's Blueyonder emails and vice-versa.

I can still access my own Blueyonder emails via my smartphone, but as my partner does not have a smartphone she can’t now access her emails herself at all.

How can we resolve this situation, i.e. by re-setting me as the primary account on our system and her back to the secondary account?