From a Home screen, touch and swipe up to display all apps.
Navigate: Settings > Apps & notifications .
Tap See all xx apps.
Locate then select the appropriate app.
If system apps aren't visible, tap the Menu icon (upper-right) > Show system.
If troubleshooting for Voicemail, select the Phone app and follow steps 5-9. Once reset, Activate Voicemail.
Tap Force stop.
Tap Clear storage.
This option may not be available for some apps.
Resetting an app does not remove saved items on the device (texts, pictures, voicemails, etc.); however saved passwords for Wi-Fi, settings, backgrounds, etc. within the app itself may be reset.