Some questions about how to get input data

[canaee]

I wanted to test it with my own data.I am a beginner.I don't know how to use rtkLib.So I want to find the input format from the output of my modul support. My modul supports NMEA output and UBX output.
But I only found position, velocity, and 3D accuracy of position and 3D accuracy of velocity from modul outputs, here I want to ask you some questions(I have seen the issue [input format GNSS #1]):
(1) I can't get the variance-covariance of the position xyz components and velocity xyz components.So can I evenly divide the three axes from the accuracy I get?
(2) I can't get covariance either.So I can set 0 to all the covariance? In addition, will this affect a lot?
(3) In issue [input format GNSS #1].you suggestion variance-covariance can assign some constants.Do you have a suggested constant?
(4) Or do you have a suggestion how I can get these values from the NMEA and UBX output?

Looking forward to your reply.
Thank you very much.