Open the Clock app
Tap Timer
Set the desired duration
Tap When Timer Ends
Scroll to and select Stop Playing
Start the timer
Play white noise in a music or white noise app
Use the built-in Background Sounds feature in Settings
Open Settings
Tap Accessibility
Tap Audio & Visual
Tap Background Sounds
Turn Background Sounds on
Select a white noise sound
Adjust volume as needed
Use Control Center to quickly turn Background Sounds on or off