Hi,
Sorry but there is no option in Theme Settings available for that.
It requires customizations and this is beyond our limitations and support policy.
It is possible to add an additional field when an FBT (Frequently Bought Together) product is added to the cart in the WoodMart theme. You can use a plugin like Advanced Custom Fields to add a custom field to the FBT product page, and then use code to display that field when the product is added to the cart.
But We have not tested this plugin with our theme and we cannot guarantee full compatibility with the plugin.
Best Regards.