How to send mavlink message to my px4 drone

hello friends, Thanks to you all, a lot of things have been resolved. However, there is one final problem that remains unresolved for me.

The problem is, I don’t know how to spawn the drone at the coordinates I want.

I referenced questions in Drone spawn position setup and How to change PX4 Gazebo (last version) home point when launching a simulation to solve the problem, but it didn’t work.
In the past I seemed to be able to get it to work fine via export PX4_HOME_LAT/LON, but now it doesn’t work. Could someone please give me some advice?
++ I change PX4-Autopilot/Tools/simulation/gz/worlds/default.sdf’s latitude/longitutde. By doing this, I was able to create it at the desired coordinates. However, what I’m doing is a multi-drone simulation, so I want to spawn multiple drones, each at the desired coordinates.