We don't know who is our domain owner

The Domain Owner is likely to be either someone within your IT or HR Team. Ask those in these teams to login to https://identity.accessacloud.com/ and see if they have the option to disable 2FA for someone else.
​
If they don't have this option, anyone from your IT can log in to their Identity account, add your company's domain to the Domains tab, and then add the verification code from Identity to your DNS record. This will prove domain ownership and make them a domain owner.