Two owners in the same account

I found a problem in one acocount: it had two users with the role Owner (don’t know how it happened).
As a result, both of them only had viewer permissions in the account.
Trying to solve this situation, I changed the another user’s role to Owner, but only one of the former owners switched to User Admin; the other remained the same,

How can I remove this role from the user “Mauro Santangelo”?
Thank you in advance!