"This is something I had encountered couple of days back and found this interesting that there is no way you can do it from the App’s window. So here are the steps to get it back :). Simple once you do it.
- Launch the People Hub. (via the Live Tile on the Start screen or via the list of apps to the right of the Live Tiles)
- Under the "All" tab, you should see a list of your contacts as well as your mug shot
- Tap your mug shot to drill down to your Me card, at which point, you will see a pin icon located in the bottom toolbar.
- That button will restore your “Me Live Tile” (this is not visible if you already have it pinned)"
from Tip: Get “Me Tile” back on Windows Phone | Vinod Kumar (Blog home), the first site I found when I googled the problem.