When you reach a dead end in Mahjong, you may see a message that says, "Try Another Path".

This means you can retry and play other tile sets and take "another path" by tapping the UNDO button in the menu bar, which also brings up the Undo Slider. Dragging the slider with your finger will let you move it to any point in your game to match a different set of tiles or start over at the beginning.

If you don't see the "Try Another Path" message in your game, you can turn it on by going to the Mahjogn menu bar > tap the OPTIONS tab > turn on SHOW DEAD ENDS.