How to change selected parameters “EKF2_MULTI_MAG”

Hello, my firmmware is PX4 1.14 and I’m trying to do a multi drone aircraft co-simulation, but I’m finding that the positioning isn’t accurate, and when I have them take off at the same altitude in offboard mode, there’s a noticeable difference between the two drones in gazebo. I want to change the parameter according to the instructions in ekf, but I can’t find the parameter “EKF2_MULTI_MAG” in QGC. Also, I changed this file “PX4-Autopilot/src/modules/ekf2/ekf2_params_multi.c” and make but it hasn’t work. I wonder how to change the parameters. Do I need to assign values to parameters with ‘CONFIG_EKF2_MULTI’ ? Thank you for your help.