In Windows 10, to configure your default apps, click Start button, Settings, System and then Default apps. This is the only supported method to manually change your default app settings.
We’ve seen behavior by some apps that have set themselves as default in unsupported ways by deleting or corrupting registry settings. Details on supported methods for apps to register file associations can be found on MSDN here. Update KB3135173 for Windows addresses the problem and resets application defaults to the initial Windows settings when registry settings are deleted or corrupted. We have worked with some of these app providers so the apps no longer exhibit this behavior in their latest versions. If a user proactively changes their default app settings using the supported method, the registry won’t be corrupted and those user settings are retained.