You may try to do that manually through your video card control panel. If you have a nVidia graphics card, go to Control Panel > Manage 3D Settings > Program Settings > Add, and then look for "TaleWorlds.MountAndBlade.Launcher" in ...\Steam\steamapps\common\Mount & Blade II Bannerlord\bin\Win64_Shipping_Client. Add that app in your nVidia settings and force it to use the dedicated GPU.
If you say that your options menu is "broken", that might mean that your resolution is too zoomed in and you can't see all the buttons in your options. If that is the case, go to C:\Users\Documents\Mount and Blade II Bannerlord\Configs and open the "engine_config" file. In that file, look for:
插入代码块:
display_width =
display_height =
Here, you can manually tell your game which resolution it should use. If it's a 1920x1080 monitor, your have to write it like this:
插入代码块:
display_width = 1920
display_height = 1080
Edit: Also, you may ignore the nVidia control panel entirely, and look for "graphics_adapter = " in "engine_config", and change the value from 0 to 1.