Yes, you can. The flow depends on your device.


iOS


On the Flight Feed cancel the Check-in. 


Then tap on the "Cancelled" word. 


Go through all the screens till the screen with Passengers. Tap on the passenger you want to edit. 


Edit info and tap Done / Next. Then submit check-in again. 


Android


On the Flight Feed cancel the Check-in.


Tap Check-in


Select passenger which you want to edit. 


Correct info and save it by going "Next". Submit check-in.