how to "enter the required Travel Document Details"

I am flying Ryanair for the 1st time and try to check-in online. However at a certain moment a page says "Enter the required Travel Document details for each passengers checking in" But there is no place/way to fill that in. During a chat from a customer service guy showing up on the web page, he advised to try with IE instead of Chrome. But that made no difference. Does anybody have a clue what to do ?
Thanks in advance

I have just made a check-in for my next flights.
When you click on the small square on the right side of the passenger name, there appear the spaces to be filled in with the nationality, passport number and validity, and so on.
But you have first to click in front of the passenger(s) name(s).
I hope this is the answer to your problem ?