Do you have multiview enabled? If so, use the options in the settings menu to enter your screen size and distance. You can also do it when in the car (Ctrl-= ? Check the control assignments). Otherwise (no multiview) find a FOV calculator that gives you the vertical angle.
This 'Mr Pix' FOV calculator has always been a good one for the various sims: https://www.projectimmersion.com/fov/