Welcome to Android Central forums. This is a very simple fix as fixes go. This technique should work for any app that you've chosen as a default app.
Open your settings and follow this path Settings>Applications>the app that you do not want to be the default anymore>Set as default>remove apps/take away permissions/revoke any apps found here.
After this the next time you open a file that was associated with that app you will be prompted to either choose an app as the default or choose a single time app.