If the Todosdays-quit smoking app is stuck on your iPhone, follow these steps to troubleshoot and resolve the issue:

1. Force Quit the App:
- Double-tap the Home button (or swipe up from the bottom of the screen on models without a Home button) to access the app switcher.
- Locate the Todosdays-quit smoking app and swipe it up to close it.

2. Restart Your iPhone:
- Press and hold the power button (and the volume up or down button on iPhone X and later) until you see the slider.
- Slide to power off your device, then wait a few seconds before pressing the power button again to turn it back on.

3. Update the App:
- Open the App Store on your iPhone.
- Tap on your profile icon in the upper right corner.
- Scroll down to see if there’s an update available for the Todosdays-quit smoking app. If so, tap ‘Update’.

4. Check for iOS Updates:
- Open the Settings app on your iPhone.
- Go to General > Software Update.
- If an update is available, download and install it.

5. Reinstall the App:
- Press and hold the Todosdays-quit smoking app icon on your Home screen until it starts to jiggle.
- Tap on the “x” to delete the app.
- Go to the App Store, search for Todosdays-quit smoking, and reinstall it.

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

7. Reset All Settings (if necessary):
- If the app continues to have issues, go to Settings > General > Reset > Reset All Settings. This won’t erase your data, but it will reset system settings like Wi-Fi passwords and wallpapers.

8. Contact Support:
- If the app is still malfunctioning after trying the above steps, consider reaching out for technical support. You can usually find help through the app’s support section or by visiting its official website.

By following these steps, you should be able to resolve issues with the Todosdays-quit smoking app. If you need more detailed guidance or alternative options, consider exploring resources such as CDC's quitSTART app guidelines - [learn more].