Yes, you can. The flow depends on your device.
On the flight feed, you need to cancel the Check-in.
Then tap on the "Cancelled" word.
Go through all the screens to the screen with passengers. Tap on the passenger you want to edit.
Edit info and tap Done / Next. Then submit check-in again.
On the flight feed, you can cancel the Check-in.
Select the passenger which you want to edit.
Correct info and save it by going "Next". Submit check-in.