First go to 'terminal' which is located at the left bottom of your Android Studio for Windows.
It will be something like this
C:\Users\ajaycarnet\AndroidStudioProjects\test4>
then type the commmand to change directory to your android sdk directory, in my case like this
cd C:\Users\ajaycarnet\Appdata\local\Android\sdk\platform-tools
Now directory is changed to this C:\Users\ajaycarnet\Appdata\local\Android\sdk\platform-tools>
type adb.exe
C:\Users\ajaycarnet\Appdata\local\Android\sdk\platform-tools >adb.exe run this command to run adb. Now install OpenCV-Manager by typing this
C:\Users\ajaycarnet\Appdata\local\Android\sdk\platform-tools >adb install C:\OpenCV-android-sdk\apk\OpenCV_3.1.0_Manager_3.10_X86.apk
Note: In my case my emulator was running on X86 architecture. install other architecture specific Apk. All APK(s) are present in OpenCV-android-sdk\apk directory. You doesn't need to download it from Internet.