You can follow these simple steps for How to Change Alarm Sound on iPhone:

Open the Clock app: Locate and tap on the Clock app on your iPhone’s home screen. It is typically represented by an icon of a clock.
Go to the Alarm tab: Once you are in the Clock app, tap on the “Alarm” tab at the bottom of the screen. This will take you to the Alarm settings.
Edit an existing alarm or create a new one: You can either edit an existing alarm by tapping on the “Edit” button in the upper-left corner of the screen or create a new alarm by tapping on the “+” (plus) icon in the upper-right corner.
Select the alarm sound: When editing an existing alarm or creating a new one, you will see the “Sound” option. Tap on it.
Choose a new alarm sound: In the alarm sound selection screen, you can browse through different categories or use the search bar to find specific sounds. Tap on a sound to preview it. Once you find the desired sound, tap on it to select it.