how can i turn off find my iphone from my computer

earlier today my iPhone 7 screen went black and I can still hear my phone calls, text notifications etc. I tried turning my phone off and on and restarting but it wouldn't even turn off/restart. now I am trying to restore my phone but I forgot that find my iPhone was still turned on on my iPhone (which needs to be off during restore from Itunes). due to the fact that my iPhone screen is completely black, I cant access the find my iPhone app on my phone to turn it off so I want to know how to turn it off using a PC. PLEASE HELP I DONT WANT TO HAVE TO TAKE IT TO THE STORE!!!