Go to Settings > Sound & Vibration > Default Notification Sound.
Freesound.org: If you want something truly unique, Freesound is a collaborative database of creative commons sounds. You can find everything from ambient city noises to experimental synth pops. Popular Categories for Alert Tones free download alert tones
Avoid "Free" sites that ask for credit card info or phone numbers. Go to Settings > Sound & Vibration >
On your iPhone, go to Settings > Sounds & Haptics > Text Tone to find your custom sound at the top of the list. Safety Tips for Downloading Tones Popular Categories for Alert Tones Avoid "Free" sites
Reduce notification fatigue by choosing softer, more pleasant sounds. Top Sources for Free Download Alert Tones
Notification Sounds: This site is perfect for professionals. It focuses specifically on short, clean, and modern alert tones that won't be disruptive in an office environment.
Open your File Manager and move the file to the Notifications folder in your internal storage.