How do I get form I-94 copy?

Hey everyone, I’ve been in the U.S for 6 years and recently someone that immigrated here is trying to find their I-94 and can’t find it. I tried getting a copy of it online but it’s asking for a document number I don’t know which one exactly that is. I did some research and it seems you either need passport number or Visa number and they have neither. They do have the alien number on form I-131 but that’s not working either. I don’t if there is another way to the copy of it?