Where can I change the default identity (set it as standard)
Are you referring to the login ID?
(I’m guessing not because that’s as simple as the email, so it isn’t and actual ID or even a username.)
Or are you referring to the account ID associated with the cloud service provider partner that shows in the Dashboard header?
(ex: email@example.com@wim.nl.tab.digital.com - note both at signs)