There are two ways around this issue.
1. Try the "forget password" on User1@company.com option
for which you will receive an email to reset the password
(assuming this is still a valid email).
2. The other option is to just put in a different Company name that no one else has used.
In fact behind the scenes we register the company name just fine.
Once you reset the password for this account, you login with that admin credential
and reset the various locations that will make User2@company.com account the new owner.
There are two locations where you can make changes: Roles and Editing Profile for that tenant.
A. After you log in and reset that password for that account User2@company.com
we highly recommend that you take ownership over it and reassociates everything
to either your account in addition to maybe creating another fail safe account
which also has access so you don’t run into the same issue if User2@company.com
is out of office in the future.
So depending on the risks you need to consider these extra precautionary measures.
B. In this scenario you will need to add the SMTP address for User1@company.com
as an alias on the User2@company.com mailbox
C. In this scenario you also do not need a new user. You need basically a mailbox where you can get email
for the specified email address during password reset. This should not be an issue if you own that mail system