Open the Photos app
Select the video you want to edit
Tap Edit
Tap the Music or Audio option if available
Choose a song from your music library or available audio
Adjust the music start point and volume if needed
Save the edited video
Use iMovie if the Photos app does not support music editing
Install and open iMovie
Tap Create Project
Select Movie
Choose the video and tap Create Movie
Tap the plus button
Select Audio
Choose Soundtracks, My Music, or Files
Add the music to the timeline
Trim or adjust the audio as needed
Tap Done
Tap Share
Save the video to your Photos app
Use a third-party video editor app if needed
Install a video editing app from the App Store
Import the video
Add music from the app’s audio library or your files
Edit the audio length and volume
Export and save the finished video