Step 1. Sign up for YouTube Studio. Step 2. Choose Content from the left menu. Step 3. Select the video that needs editing. Step 4. Select Editor from the left menu. Step 5. Choose Audio and use the search filters to discover a new audio track. To hear a music preview, click Play. Step 6. Click ADD when you locate a song you like. The song will show up in a blue box in the editor. You can move the box to alter the song's starting time. Drag the box's edges to alter how much of the music plays. Use the zoom options Zoom in for more precise adjustments. Step 7. Click SAVE when you are completed.