Where add a specific line in the cmake file?

Hi! I’m trying to add my own simple application in the PX4 Firmware but when I launch it with the command “make px4_sitl_default gazebo”, I can’t see my new command in the list I can use so I can’t make it work. What do I have to add in the cmake file and where please? (It’s my first experience in robotic and development, please be indulgent)