Stop auto mode and RTL and start at point we stop (continue the mission )

hi guys
i have some problem i want in during of auto fly (auto mode) use RTL and after landing i want to continue the old mission and start from the point we switch to RTL mode
can any body help ?

In qgroundcontrol , click on an mission item to go to after takeoff.
In apmplanner2 use “go to mission item” and select a number.
In MAVProxy enter “wp set 8” to go to 8

i need to do it automatic when i put it back to auto get to the last position