Navigate to the 'Apps' page on Bookvault
Press the button 'App Settings'
You will get a dialogue box like the below.
Toggle the 'Free Shipping' and hit update settings
This should update the shipping profiles on your store, this can take up to 1 hour to update and reflect on your store.
Please note: The order would be sent on the cheapest delivery service, and Bookvault would still charge you the related shipping charge for this