You can adjust the default settings for all meetings created by Bookwhen's Zoom integration. Once you save your settings, any changes will automatically be made to all current and future Zoom meetings.
You'll be able to specify these settings when you first integrate with Zoom. To review and adjust your settings at any point:
Go to Setup > Integrations
Click 'View integration'
Now adjust your settings and click 'Save settings' (screenshot below)