If you can boot up into Windows that means you can at least check if the card has been detected. Why can't he download drivers for it? Check the nvidia site for drivers and you'll find them easily there if your brother doesn't know how to do it then send it to him.
As for checking if the gpu has been detected properly go into Device Manager and check under "Video Adapters" if Windows hasn't already downloaded drivers for it(it must have if it's on Windows 10). If it hasn't been detected, then all you have to do is to download the drivers from the nvidia site and install them.
Good Luck!