Coordinates Home

Hello,

I hope this is the right category for this question, if not let me know.

I wanted to change the RTL coordinates during an automated or manual flight.
The idea is that the coordinates are linked to a (slowly) moving truck and if there is a failsafe (i.e. loss of RC) that the drone goes to the new RTL coordinates.

I have the GPS coordinates of the car so I could manually enter them in Mission Planner but I don’t know how to do this.

I tried adding an RTL waypoint & turning off the RC but the drone always returned to its home point (where the battery was connected).

How can this be done?