Help with the potential new claim form

So they offered what I would assume all the people who files an appeal against the overpayment got a chance to file for that potential new claim to help skip over the appeal process. The issue I'm having is they want to know about a job I had almost 3 years ago that I gave information for at the time of my application but I don't have that information anymore. Poor organization on my part means I have no idea on exact dates or my gross pay so I can't fill out that section of the form. Is there anything I can do about this since I know they will cross check the info and I'm afraid if I get any of it wrong compared to the info they already have my benefits would be denied entirely and I'll have to pay back all the money I don't have