You can use the RandomNumberGenerator class to generate two float values, x, and y.
Those values will be within a specified range, so for your map generate a x between 0 and 1344-1
and a y between 0 and 768-1.
Note that the upper bound is minus one, because you want to find a point inside the map.
Then once you have the values, you need to check if the point is occupied, and if there is something already there, search the area around the point for a free space.
Once you find the free spot, you can just move the Area2D to it. You don't have to free the Area2D and make a new one, moving it right to the new spot should have the same affect.