Hi there! I'm sorry to hear that you're having trouble signing in to the Fly Delta app. Let’s work together to resolve this.

First, could you please tell me if you’re receiving any specific error messages when you try to log in? It would also help to know if you've recently changed your password or if you can access your account via a web browser.

In the meantime, here are a few basic steps you can try:

1. Check Your Credentials: Make sure you’re entering the correct username or email and password. Sometimes a small typo can cause issues.

2. Reset Your Password: If you're unsure about your password, you can reset it. Look for the "Forgot Password?" option on the login screen.

3. Update the App: Ensure you’re using the latest version of the Fly Delta app. Visit the App Store, check for updates, and install any pending updates.

4. Internet Connection: Make sure your iPhone is connected to the internet. You can try switching between Wi-Fi and mobile data to see if it makes a difference.

5. Clear App Cache: Sometimes clearing the app's cache can help. You can do this by uninstalling and reinstalling the app.

Let me know if you've tried any of these steps or if you're still facing issues. I’m here to help!