Arduino to switch modes of the pixhawk

Hey everyone

I am currently building a tracked rover for a school project and it is controlled with a pixhawk autopilot and i would like to be able able to switch “flight modes” (from auto to manual/manual to auto) with an arduino mega when it detects an object infront of it ( I have the code for the distance sensors already) however i am struggling with the code to send signal to switch modes through MAVLINK ( beginner to the communication between the two) so i was wondering what a code looks like , if anyone has examples as to then just edit to my configuration

I was also wondering how to control a gimbal from the pixhawk using my ground station controller (9XR Pro)

Thanks in advance