: Use a file manager app to copy or move your downloaded MP3 into the internal storage folder named "Notifications" .
: To set a sound for just one app (like TikTok or WhatsApp), go to Settings > Notifications > App notifications , select the app, and tap Notification categories to change the sound for specific alerts. Setting Custom MP3 Notifications on iPhone Download notification 125767 mp3
Once you have your MP3 file, setting it as your default or app-specific alert varies by device: Setting Custom MP3 Notifications on Android : Use a file manager app to copy