How to increase right click zoom in Shooter Game?


I am trying to create a sniper within the game and want to know how, if possible, to decrease increase the zoom that is already done when holding the right mouse button. I have no experience with C++, but I am pretty sure that this would require changing the Camera Update function. My guess is that I have to decrease the FOV within the function so that when holding the right mouse button, the zoom will be tighter, essentially increasing the zoom.

Thank you.