From the event “dashboard” click on the “Onsite check-in” card. 

Now click on the “Locations” tab on the left-hand side of the screen.

This will list all the check-in locations for your event.

Select the desired location and click on the “edit” button. 

Make sure the “can check-in” checkbox is checked. 

Under the check-in configuration, check the “ Restrict Check-In Count” checkbox.

Fill in the “check-in user limit” and click on save. 

This will limit the number of check-ins for the selected location.