Follow the below steps to assign a session to Scan Attendee user.
The Event Admin has default rights to scan the Attendees. if would like to add more user to scan please add scan attended user.
Step 1: Go to the App Settings under the Event App.
Step 2: Select the Scan Attendee Tab.
Step 3: Select the Assign session to user Tab.
Step 4: Enable the scan permission for the user and save.