Level Select
On the Main Menu, tap [Up], [Down], [Left], and [Right] on the D-Pad. After doing so, tap "New Game". On the resulting message, tap "Yes". If done correctly, a Level Select menu should appear instead of Green Hill Zone Act 1.
Hints
Play as Any Character
To access this you first will have to enter the level select menu by starting a new game with no save. Then you will have to press the sega logo when it appears in the order of s-e-g-a. When it says to start put two fingers on the screen and swipe up. Then where you see player you can select the character you want. 01 for sonic, 02 for tails, 03 for knukcles, 00 for sonic and tails.