Hi there! I understand the COMMAND PRO app isn't opening on your iPhone running iOS 18.6. Let's work through this together.

First, can you tell me a bit more about what happens when you try to open the app? For example:
- Does the app crash immediately, freeze, or show an error message?
- Has it ever opened successfully on this device before?
- Have you tried restarting your phone or closing the app completely before reopening it?

Once I have those details, I can guide you through the most effective steps. Meanwhile, here are some general troubleshooting tips you can try:

1. Force close the app: Double tap the Home button or swipe up from the bottom to bring up the app switcher, then swipe the COMMAND PRO app off the screen to close it. Then try reopening it.

2. Restart your iPhone: Sometimes a quick reboot helps clear any temporary glitches.

3. Check for updates: Go to the App Store and make sure the COMMAND PRO app is updated to the latest version compatible with your iOS.

4. Delete and reinstall the app: If the above don’t work, uninstall the app by holding its icon until it wiggles, tap the ‘x’, then reinstall it from the App Store. This often solves deeper issues.

5. Check device storage: Make sure your phone has enough free space, as low storage can sometimes block apps from opening properly.

If you've already tried these, let me know which ones, and I can suggest more advanced steps next. I’m here to help!