When your phone gets reset or you have a new Windows Phone you might want to get back the old apps you had downloaded in past. Here it is as easy as candy.
1. Go to http://www.windowsphone.com/
2. Login using the same Microsoft Account which you are using in the Windows Phone
3. You need to enable “Find my Phone” from Settings.
4. Then go to “Purchase History” https://www.windowsphone.com/en-us/my/purchase-history
This would show you the list of Applications you had installed earlier. You can simply click on reinstall and it will push them to your phone