my i phone is stuck on world clocks. help please

If your iPhone is frozen in an app, you can try to close the app completely by pulling the screen from the bottom up to the middle of the screen, and then swipe the app up and away.

This will close the app completely and hopefully the app won't freeze again.

If your screen is completely frozen, you can do a Forced Restart like this:

1. Press and quickly release Volume Up

2. Press and quickly release Volume Down

3. Press and hold the Side Button, the phone will restart. Release when you see the Apple Logo.

Find more information here:

If your iPhone won't turn on or is frozen - Apple Support