Using google translate, my english is not good
a solution is there
Step 1: go to where the game folder is (mainly it is on disk C and in x86 program files) create an additional folder in that folder, give it any name and move the game folder (Call of Duty Modern Warfare) to the one you made just believe
Step 2: when opening battle.net, it will not find the game, you must have the option to “Add game” or “Search game” and select the folder you created, if the problem continues, run battle.net as administrator, if the problem persists, look for another solution