Within the Daily calendar page tap on the ‘level button’ (located at the top of the page - the one that displays the current level, for example, Medium) which will slide out a drawer containing all modes and levels. Simply tap on the one you wish to play.

A silver or gold star next to a level name indicates that you have played at least one game for that level in the corresponding calendar month. Whenever you are re-entering the calendar page after a completed game, you will be sent automatically to the current month of the last level played.