My passenger window makes a loud rattling noise every time i close my door. after removing the door panel, I found this is due to the rear bottom bolt/flat nut that holds the window on the regulator assembly to be very loose.

Im trying to tighten the nut/bolt but am having a hard time doing so because the "nut" part is flat (maybe 1-2mm thick), about the size of a .50 cent piece and has 4 small holes around the outside which makes me believe I need some sort of key or special tool to tighten it. I got it semi tight using tiny pliers but its not at tight as it should, window still makes some noise when closing the door but its MUCH better than before...

Does anyone know what type of key/tool I need to tighten down this flat "nut" with 4 holes in it? Ive attached a photo for reference from a service manual. The flat nut is what i tried to draw with the 4 holes, the center circle is where the bolt goes in from the other side which is very easy to get to (10mm)