The section on page 4 of the manual, "Move a colonist to a different square in the area view" is somewhat unclear and I have never found it work as directed anyway.

To do this using the mouse all you need to do is click and hold the left mouse button on a square on the map that you want the unit to move to.

That's correct.

I discovered it years ago in the DOS version when sometimes my colonists moved to undesired destinations.