If we installed two or more apps which does the same purpose, for example Video Player, Browser, etc. Then, the OS will pop-up a dialog with the available apps which will handle the operation. You can select the preferred app to do the operation Always or Just once
If you made a wrong choice or you wish to clear the app just follow the steps.
How To Clear Default Application in Android ?
1. Go to Settings -> Apps
In some android versions go to Settings -> Applications -> Manage Applications to get the apps list.
2. Find the app you want to reset and select it.
3. Finally tap Clear defaults button.