The player on turn can be set by clicking the small checker icons below the board. See figure below.
Clicking the White checker image will set White on turn, clicking the Black image will set Black in turn.
Note that setting the turn sets the turn before the dice has been rolled. If there is a dice present at the board, setting the turn will remove the dice rolled. In this way you can set up a position to be a cube decision evaluation instead of a move decision evaluation.
The turn can also be set by choosing Game->Set turn. Both these methods for setting the player on turn can also be used without being in edit mode.