I really hate this stuff, I actually get stressed out when I know I need to work with it. I have tried everything, putting it in hot water, blowtorch, microwave, it is just the pits to work with thi...
I used to build RV's back in the day after HS...Coachmen.
Anyway, we used a plastic stick, similar to a putty knife but about 1/2" wide. You would just it started and use the stick on one side and your fingers on the other to guide it in.
It must the the brand, quality and wrong size for to be difficult, it should just slip right in. It is cosmetic screw covering, serves no other real function.