Figuring this thread might get quite a few views, so I'm posting a slightly more detailed description along with a screenshot. :)
To restart the game, you'll first need to tap on the main
MENU, which is the little white star symbol in the upper-right corner of the screen. Then tap the
up arrow symbol on the bottom of the screen to get to the
LOAD screen shown in the screenshot below. You'll see that the screen has several circles (save spots). Now tap on the first circle (numbered '0') showing the observatory house of the space gnome, and then tap the check mark to confirm and the game will restart from the very beginning.