Clear an app’s default-action preference so Android prompts you to choose again, instead of silently reopening a stale default (e.g. an old mail client after installing a new one).
The screen also has link-verification toggles above the default-preferences section — unrelated setting, leave them alone. Clearing the preference doesn’t uninstall or disable the app; it only resets the app-picker prompt for that action.
Cheatsheet
Clear a default app
Settings→Apps- Select the app .
Open by default→Other default preferences→Clear default preferences