How we can check if the user added through ADMIN console

The audit log answer suggested before is the first thing you should check.  Also you should consider who has ADMIN access in your UAT environment - if there are enough users with ADMIN level accounts that you're not sure who added a new user, you should probably do a review of your access levels and change all but a specific few users to BASIC level accounts.

The audit log answer suggested before is the first thing you should check.  Also you should consider who has ADMIN access in your UAT environment - if there are enough users with ADMIN level accounts that you're not sure who added a new user, you should probably do a review of your access levels and change all but a specific few users to BASIC level accounts.