I have polar PRO ND filters.
found that i should have these settings

ISO 100.
Fps 30 Shuterspeed 60 and fps 60. Shuter 120
What  should i set aperture settings  to?

Well I think that depends on the ambient light available.  You can use the histogram in the DJIGO4 app or just look at the image on the device.  Being that the ISO and shutter are constants, you only have the f-Stop to vary to get the right lighting.  I think you can use the EV setting too.  I am new at this camera as well.  The ND filter will have numbers like 8, 16 , 32 etc that indicates the shading of the filter.  The higher the number the darker the shading I believe.  The higher the f-stop (smaller aperature) the longer the focal length.

Use the EV value try to keep it just under -0.3EV rather than over exposed, use what ever aperture is needed to achieve this. Don't just rely on what you see in the device screen.

another fun tidbit, certain ND Filters or CPL filters or UV filters don't fit into the gimbal holder so you always have to screw and put on the original one


for setting you have to really record and then put into your editting software to see and get a good feel for what you want. (as flat as possible, as Canon vibrant as possible etc etc)

Aperture, in this case, is used to properly expose the scene. As stated above histogram is your friend. Also, the overexposure stripes. Keep in mind depth of field changes with the aperture. Not drastically on the P4P but it does change. Also sharpness from edge to edge changes based on aperture settings. Every setting, Shutter speed, ISO, and Aperture have their benefits and drawbacks at each end of the spectrum. There isn't one setting for everything. Understanding how to balance the exposure triangle and achieve the desired effect is really what you are after. for instance, there may be a time where you need or want to break the shutter speed rule or bump the ISO up instead of opening the aperture.