default raytracing demo scene not rendering the same, full of noises

Development Rendering
1

Hello

I have this project provided by Epic game:

but when I open that project with all requirements, Gpu (2080 super), windows version ( all set) , I have lots of flickers especially for some material.
how they manage to render this beautiful render?

is there specific setting should I tweak to get the same render?

thank you in advance