How to eliminate Apple TV on opening of Photos slide

Thanks but I needed detailed steps which I just found:

Permanently change the app used to open a file

1. On your Mac, click the Finder icon  in the Dock to open a Finder window.
2. Select the file, then choose File > Get Info.
3. You can also Control-click the file, then choose Get Info.
4. In the Info window, click the arrow  next to “Open with.”
5. Click the pop-up menu, then choose the app.
6. To open all files of this type with this app, click Change All.

Thanks, but how do I change the default app?