Return timer buttons Smeg S600 Oven after removal to clean?

I was cleaning my old Smeg oven and decided to pop the 5 plastic timer buttons off ( pulled out easily)to soak and am unable to click them back into place. They aren't broken and look as though they should just press back in. Unfortunately proving difficult, is there an easy way to do this? I would be very grateful for help as I don't like using smoke as a timer.
Thanks Vivienne

Vivienne
July 2009