You can use our 'Check-in Form' extension template to check in event attendees. This form uses a login page with barcode/QR code scanning capabilities to bring up a user's record, and prefills an auto-generated "Check-in Time" field with the current date and time.
After a successful check-in, a newly created Check-in Form reloads the Login/Lookup page so the next attendee can scan their code. The default Reload Delay is 5 seconds. To change it, open the form settings, expand Submission Actions, and adjust Reload Delay.