This option will only affect the account that you are currently signed in to.
You do not need to be an administrator to do this option.
3. To "Undo" Restore Windows Photo Viewer for Only Your Account
This is the default setting.
5 Double click/tap on the downloaded .reg file to merge it.
6 When prompted, click/tap on Run, Yes (UAC), Yes, and OK to approve the merge.
7 You can now delete the downloaded .reg file if you like.
8 If you selected to undo restore Windows Photo Viewer, then select a different app (ex: Photos) as the default app under Photo viewer in Settings. (see screenshot below step 9)
9 If you selected to restore Windows Photo Viewer, then select "Windows Photo Viewer" as the default app under Photo viewer in Settings. (see screenshots below)
If you do not see the restored Windows Photo Viewer in Default apps, then close and reopen the Default apps settings page to refresh it.