Like I said, the "click" is an input mapping. You can create a input map for "right_click" in the project settings input tab. This is fundamental to working in Godot, so you should learn how this works.
https://docs.godotengine.org/en/stable/tutorials/inputs/input_examples.html
In terms of movement, the code I posted in the last post will get the selected units. This code can be called anywhere, probably on _input() would be a good idea.
func _input(event):
if event.is_action_pressed("right_click"):
move_selected_units_to(event.position) # this is a function you create
Then you have to so the movement movement, there are many methods to move objects. Again this is fundamental Godot and game programming 101. How to move a Sprite. You could use a Tween, you could use lerp or linear_interpolate. You can simply figure out the difference in position (from the last position to the right click position) and then add that value to the position of each tank a little bit each frame (multiply by delta). But please look into it, I can't code the whole game for you.
