Mavlink Messages in Mission Planner

I know mission planner sends mavlink messages to the drone, but I thought I could type in my own message. I want to send a command_long message but I don’t know how. Everything I find online talks about the parameters in the message but not how you actually send one.

I am using the current version of mission planner. I am using a blue cube h7 with the latest copter firmware.

This software is new to me, so any information is appreciated. Thank you