To reset SMS settings on your iPhone, follow these steps:
1. Open the "Settings" app on your iPhone home screen.
2. Scroll down and tap on "Messages" (for iOS 13 and later) or "Messages & FaceTime" (for iOS 12 and earlier).
3. In the Messages settings, scroll down to find the "Message Options" section and tap on it.
4. Look for the "Keep Messages" option. By default, it is set to "Forever". Tap on it to change the duration.
5. A pop-up window will appear giving you options to choose from, such as 30 days or 1 year. Select your preferred timeframe or tap on "Delete" if you want to remove all messages permanently.
6. After selecting the desired duration, the Messages app will prompt you with a confirmation. Tap on "Delete" to complete the process.
By following these steps, your SMS settings will reset, and your messages will be deleted based on the chosen duration. Remember that resetting SMS settings will only affect the preferences and storage of your messages. It won't impact any other settings on your iPhone.
Please note that while the provided steps are accurate based on the current information available in 2023, it is always recommended to check for any possible software updates and changes in the iOS user interface to ensure the instructions remain relevant.