Okay, so you're gonna have to :
1st : Right click on No More Room in Hell and click properties, go to local files, and browse local files. Then click on nmrih and cfg.
2nd : Copy any file and paste it inside. Then remove all the text inside and rename it, then paste this inside

sv_cheats 1
mat_dxlevel 80
mat_dxlevel 80
cl_ragdoll_collide 0
mat_picmip 4
r_WaterDrawReflection 0
r_WaterDrawRefraction 0
mat_wateroverlaysize 8
r_lod 5
mat_fullbright 1
mat_diffuse 5
mat_bumpmap 0
r_shadows 0
mat_fullbright 1
mat_forceaniso 0
mat_forcehardwaresync 0
mat_reducefillrate 0
mat_mipmaptextures 0
mat_filtertextures 0
mat_bloom 0
mat_envmapsize 32
mat_envmapgasize 8
mat_antialiasing 0
cl_phys_props_enable 0
mat_filterlightmaps 0
mat_showlowresimage 1

After that, just save your changes and start up the game.

Okay, once you're in-game, just go on a server that has sv_cheats turned on or just make your own server. Then type this into console : "exec *Potato Graphics file name*", but type it without the brackets (Theese things ") and replace the *Potato Graphics file name* with the name of the potato graphics cfg file that you made.

(P.S. The section with Sv_cheats 1 is optional)

And that's it! Now your game will look like this. And you can enjoy NMRiH on potato PC graphics! :p