You can mute the voiceover by prompting the magic box to do so, or do it from the "Settings" option:
Decrease voiceover volume to 0
Mute the voiceover
From the Settings section:
1. Select ‘Edit’, then head over to ‘Settings’.
2. Here, you can adjust the "Voiceover Master Volume" to your preference.
💡 Note:
Muting the voiceover in specific parts of the video using the Magic Box feature is not yet available.
As a workaround, you can use the script section to add pauses between chapters, as shown here.