Ok well first things first you have to download Horizon and it will be here:
[ Register or Signin to view external links. ]

After that move your profile to usb and when done put usb in computer

Next after that go to YouTube and search Minecraft Xbox map downloads and watch one of the videos and go to the description and it should have a link to media fire or ad.fly but if that appears hit skip add and it will redirect you to mediafire.

After that you hit download then at the bottom of your screen it should say how you would like to save the map hit the drop down arrow and hit: save as. then hit the dowloads when another tab appears and just save it.

Next load Horizon and click on gamer profiles, hit your profile once then click inject new file and your saved download. Load that up and it should have your name appear again.
Double click your gamertag and there you go. Then put your Profile on your xbox