iOS App Stability Fix

I need a skilled iOS developer to diagnose and fix stability issues with my app on older iPhones. The app currently crashes immediately on launch.

Key requirements include:
- Diagnose crash issue on older iPhones
- Fix stability problems
- Update app to latest iOS SDK if needed

Ideal skills and experience:
- Proven iOS development experience
- Familiarity with troubleshooting app crashes
- Knowledge of iOS SDK updates
- Experience with backward compatibility for older devices

Please provide a clear plan and timeline for resolution.