Google Maps not auto-rotating is a common issue faced by both iPhone and Android users. This problem can be frustrating especially when navigating unknown routes. However, there are several ways to fix this issue.

For iPhone Users:

1. Check Location Services: Go to Settings -> Privacy -> Location Services, and ensure that they are turned on for Google Maps.

2. Enable Compass Calibration: Navigate to Settings -> Privacy -> Location Services -> System Services and turn on Compass Calibration.

3. Update the App: Make sure you’ve updated Google Maps to the latest version from the App Store.

4. Restart Your Device: Sometimes a simple restart can fix minor software glitches.

5. Reset Location & Privacy: Reset your location and privacy settings by going to Settings -> General -> Reset -> Reset Location & Privacy.

For Android Users:

1. Check App Permissions: Go to Settings -> Apps & notifications -> Advanced -> App permissions -> Location and make sure Google Maps is allowed access.

2. Calibrate Your Compass: Open Google Maps and follow the on-screen instructions to calibrate the compass by moving your phone in a figure 8 motion.

3. Clear Cache and Data: Go to Settings -> Apps & notifications -> See all apps -> Maps -> Storage & cache and then hit Clear Cache followed by Clear Storage.

4. Update or Reinstall: Update Google Maps via the Play Store or consider reinstalling it if the problem persists.

5. Restart Your Device: A restart can resolve temporary software issues that might be preventing proper functioning.

By following these steps, you should be able to resolve any auto-rotating issues with Google Maps on your iPhone or Android device, ensuring a smoother navigation experience during your travels.