By the looks of it (slotted mounting holes) he should be able to slide the tray away till clear of the rail, tighten that side of the tray, then push the other side of the tray inwards till clear and tighten.
It’s not that complicated, the tray has flex.
Or simply grab the tray rails and squeeze it together till it sets clear of the block pan rails.
Or just push the pan down over the rails as is.
Easy peasy to make work.