Hi @Flory10
When you go to the Photo Tour page the photos show up arranged according to the rooms. If you click on one of the photos there, one sees no option to make it the cover photo. I think that's what was bothering you, and I had the same problem a while ago.
It seems you can only change the cover photo if you click on "all photos" (next to the Photo Tour heading). Then click on the photo that you want to make your cover photo and you will see the option "Make cover photo" to the right of the photo.