A. 1. Force close the app: Double-tap the home button (or swipe up from the bottom of the screen on newer iPhones) to view all open apps. Swipe up on Planimeter Pro to close it. Then, reopen the app to see if it works properly.
2. Restart your iPhone: Hold down the power button until you see the 'slide to power off' option. Slide to turn off your device, wait a few seconds, and then turn it back on. This can clear temporary glitches that may cause the app to crash.
B. 3. Check for iOS updates: Go to Settings > General > Software Update. If an update is available, download and install it. Sometimes, app crashes can be resolved with the latest iOS version.