To change the default alarm sound on your iPhone, you can follow these steps:
Open the Clock app on your iPhone. It's the app with a white icon and a clock face.
Tap on the "Alarm" tab at the bottom of the screen.
Tap on the "Edit" button in the upper-left corner of the screen. This will allow you to edit your existing alarms or create a new one.
Choose the alarm for which you want to change the sound. If you want to create a new alarm, tap the "+" button to create a new alarm first.
Tap on the "Sound" option. It is usually located below the time settings for the alarm.
In the sound selection screen, you'll see a list of available alarm sounds. Scroll through the list or use the search bar at the top to find the desired sound. You can listen to the sounds by tapping on them.
Once you've found the sound you want, tap on it to select it.
To confirm and save the changes, tap on the "Back" button in the upper-left corner of the screen. Alternatively, you can tap "Save" in the upper-right corner of the screen if you were editing an existing alarm.
That's it! You have now successfully changed the default alarm sound on your iPhone. The new sound you selected will play when the alarm goes off.