Your monitor resolution is usually in the options menu built into its buttons if you don't know what it is, or you can search "display resolution" in the windows search menu and the native resolution of your monitor will be the one labelled "recommended".

If you mean can't access/find the appdata>local folder, search %localappdata% and it will open directly. The res.txt file is a simple text file you can edit and save with notepad, just hit enter and add your native monitor resolution to a new line (in the pictured example I added 1680x1050- you really don't need to do anything special) and save.

If the assets folder/res.txt is not there in the votv folder, run the game as admin- right click the VotV.exe, go down to properties, in properties go to the compatibility tab, and check "run as administrator" on. Run the game, allow it when the admin access pops up, once you get to the main menu you can quit and it should now have generated the missing folders and files.

If you just don't know how to change your resolution, it's in the video settings (I think is what it's called, haven't gotten to open the game in a few weeks) of the VotV options, same options tab you would change to fullscreen or windowed. Change the resolution to your native monitor resolution and apply.