...\Call of Duty Black Ops III\players\config.ini
FullScreenMode = “0” // 0 to 2
WindowSize = “1366x768” // any value
go here: Steam\SteamApps\Common\Call of Duty Black Ops III\PlayersIf config.ini does not exist, open a new notepad and putCode: [Select]FullScreenMode = “0” // 0 to 2 for windowed modeCode: [Select]WindowSize = “1366x768” // any value for size of windowrename the new notepad to config.ini
Try going to its folder in Steam and openCode: [Select]...\Call of Duty Black Ops III\players\config.iniAre there any resolution options in there?