1/ Place a crosshair on the mechanical layer at the centre point where each LED is required.
2/ When you "copy" your "room" you will be asked to set a reference point. Set the reference point exactly at the centre point of your existing LED in your first channel.
3/ When you "paste" your room (to form your second channel), your visual crosshair will be at the centre point of your LED. Your room will be "floating" on your cursor.
4/ Move your room such that your LED centre point is on top of the crosshair you placed on the mechanical layer. Fix the room onto the PCB by pressing the mouse button.
5/ Rinse & repeat steps 3/ & 4/ until all your "channels" are complete.