See the issue on the topic here Need Support Figure of eight (8 figure) loitering by QGC · Issue #12778 · mavlink/qgroundcontrol · GitHub
Basically you’re adding a command like the “Orbit at Location” item shown at that link when you click the map. As to how to do it, the easiest way is to see how QGC implements that Orbit command and copy the behaviour.
Also even if i make changes on QGC, I will need to make changes in common.xml file as well right on PX4 side?
No, you don’t have to make any changes to PX4 on simulator (at all). You would need to do a custom build to enable it on hardware - that is all covered in the PR I linked - [this one](https://github.com/PX4/PX4-Autopilot/pull/26194)