1) Basically, you can get mag data using bmi160_extract_aux function. But, need to compensate using below fucntion.
2) If you have your own algorithm and want to use accel and gyro data for compenstation, you can use it.
You also can get a data using bmi160_extract_gyro, bmi160_extract_accel.
Please check below url and the attached file.
( The attached file is updated version of the url guide )