I don't know of an "easy guide" for 9DOF sensor calibration. Calibration requires several independent steps, and some technical skills.
This 9DOF sensor works as well as any I've used
A working Mahony filter for the ICM-20948 can be found here, with two calibration programs (one Python, one C) and instructions.
Magnetometer calibration example for a difficult case: https://forum.pololu.com/t/correcting-the-balboa-magnetometer/14315