Open Settings
Tap Privacy & Security
Scroll down and tap Developer Mode
Turn on Developer Mode
Restart the iPhone when prompted
After restart, confirm Developer Mode
Enter your passcode if asked
Wait for the device to finish enabling Developer Mode
If Developer Mode does not appear, connect the iPhone to a Mac with Xcode installed
Trust the computer on the iPhone
Open Xcode and pair the device
Recheck Settings for Developer Mode
If needed, update iOS to the latest version