Self Check-in for Event Guests needs to be turned on at the Event Category level
You must be an Organisation Admin to turn on Self Check-in for Event Guests at the Event Category level
Once is it turned on, you have to activate it on each event you want to use it on.
Steps
Select My Apps in the top menu
Select Event Categories
Press Edit next to the Event Category you want to edit
Scroll down to the Event Attendance section and tick the box to turn on Self Check-in
Press save
That’s it. Now you can activate Self Check-in on each event you create using this Event Category.