Can I change resolution without going in to the game?

Yeah I just wanna know what is stated in the title. I just recently got a new monitory and it dosen’t support the resolution the game had the last time I played it. I can’t change nor shut the game down. The monitor just goes black and there is this moving window that says “Change computer resolution etc.”. So is there anyway to change the resolution without having to start it and change it in the options menu?

Yea, go in steam. Right click Garrysmod. Click Properties. Then, click Set Launch Options.
Type this in the box:
+width 1024 +height 768 Press ok. Then, double click Gmod, the resolution should now be 1024x768