First, go to Settings > General > Date & Time. The first option is to decide whether or not you want 24-Hour Time or not. So if you prefer 17.00 hours instead of 5.00 pm, then toggle this option
Open Settings. Scroll to Calendar and tap Time Zone Override. Toggle on the Time Zone Override bar. Method 4. Set Date & Time According to Location Time Zone Settings. Another method to fix the iPhone that automatically changes the time zone is to base it according to the location time zone settings.
First, go to Settings > General > Date & Time. The first option is to decide whether or not you want 24-Hour Time or not. So if you prefer 17.00 hours instead of 5.00 pm, then toggle this option