Castle guard new wave button

Castle guard. What does the new wave button do? There are now three buttons. Looking at the wave there is the upgrade button in the middle the blue symbol on the right and a new button on the left, looks like a scroll.

Thank you.

Zippy

Fill one wave as usual (don’t use button on the right, it fills the wave with random (?) troops).
Then press the button on the left to copy the wave. The left botton changes on all other waves,
by pressing it you paste the copied troops to that wave (can be done for more than one wave).
Additionally you can drag and drop troops to fill waves.