First of all, you'll need to complete the settings for the Inventory page. Navigate to Pages in dashboard menu and edit the page that you defined as listing type inventory page.
Switch to the WPBakery Page Builder editors and click Add Element.
Open the Motors Listing Types tab and select the MLT Classic Filter element.
Choose an appropriate listing type and a number of listings to display in the MLT Classic Filter settings.
Save changes and update the Inventory page. The page should display a filter box and search results area.