To resolve the issue of the Stealth Fitness app not opening on your iPhone, follow these detailed troubleshooting steps:

1. Close and Reopen the App:
- Double-click the Home button (or swipe up from the bottom of the screen on iPhones without a Home button) to access the app switcher.
- Find the Stealth Fitness app and swipe it up to close it.
- Wait a few seconds, then reopen the app to see if it launches properly.

2. Restart Your iPhone:
- Press and hold the power button until you see the “slide to power off” option.
- Slide to turn off your device. After it powers down completely, press and hold the power button again to turn it back on.

3. Check for App Updates:
- Open the App Store on your iPhone.
- Tap on your profile picture in the upper right corner of the screen.
- Scroll down to see if there are any updates available for the Stealth Fitness app. If there is an update, tap “Update” next to the app.

4. Update iOS:
- Go to “Settings” > “General” > “Software Update”.
- If an update is available for your iOS version, tap “Download and Install”.

5. Check Storage Space:
- Go to “Settings” > “General” > “iPhone Storage”.
- Make sure you have enough available storage space. If storage is low, consider deleting unused apps or files.

6. Uninstall and Reinstall the App:
- Press and hold the Stealth Fitness app icon until the options appear.
- Tap “Remove App”, then confirm by choosing “Delete App”.
- After the app is removed, go to the App Store, search for "Stealth Fitness," and reinstall it.

7. Reset Network Settings:
- Navigate to “Settings” > “General” > “Transfer or Reset iPhone” > “Reset”.
- Choose “Reset Network Settings”. Note that this will erase saved Wi-Fi passwords, so be prepared to re-enter them.

8. Contact Support:
- If the app still won’t open after all these steps, consider visiting the Stealth Fitness website for assistance or contacting their support team directly for further troubleshooting options - learn more - learn more.

By following these steps, you should be able to resolve the issue with the Stealth Fitness app not opening.