A default app is the program that Windows uses automatically when you open a particular type of file, such as a song, movie, photo, or webpage.
For example, you might have more than one photo-editing app installed on your PC. You can choose one of them to be the default app that starts whenever you open a photo.
Swipe in from the right edge of the screen, tap Settings, and then tap Change PC settings.(If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, click Settings, and then click Change PC settings.)
Tap or click Search and apps, and then tap or click Defaults.
The default you choose will only apply to your account and won't affect other accounts on this PC.
On the defaults page, tap or click a current default app. If there is no default, tap or click Choose a default.
Tap or click a new default app.
The default email app must be one installed on your PC. You can't use a web-based email service, like Outlook.com, Gmail, or Yahoo! mail as the default email program.
You can fine-tune default apps based on the file type or protocol. For example, you can have all .jpg image files open using one app, and .bmp image files open using a different app.
On the defaults page, tap or click Choose default apps by file type, or Choose default apps by protocol.
Tap or click a current default app, – Or – If there is no default, tap or click Choose a default.
When you change a default app for a file type or protocol, you can't leave it blank. You must select a new app.
You can make a program inaccessible without uninstalling it. For more info, see Set program access and computer defaults.