Uploaded knowledge but not available

I have upload my files and I want to create quiz but when I’m going to “quiz” my files are not available.

So I’m trying to uploaded them again but this time in the “quiz session” and it says that I can’t because they are already uploaded.

I can’t find out how can I use them in the “quiz session “ and as I saw from other people who use the app they must have been already

there for me to choose them.