I can see that you already received a reply via ticket system. I will still provide the solution/guide on this post in case anyone else has the same questions.
In order to add fitment attributes to an Amazon item, you need to use the following attributes when creating the Amazon listing: Part type ID, Vehicle Fitment Code, and Vehicle Fitment Standard. You can find these attributes for corresponding categories in the Amazon configurator. These attributes can also be filled in automatically with the information from item Extended Properties.
Documentation on item extended properties: https://www.linnworks.com/support/inventory-management-and-stock-control/my-inventory/managing-inventory-items/extended-properties
Documentation on using item extended properties on an Amazon configurator: https://www.linnworks.com/support/listing-management/listing-via-my-inventory/amazon/configurator#Attributes
Images of how these attributes appear on the configurator attribute list:
Hope this helps.
With Best Regards,
Linnworks Technical Support
How to have Products ( auto parts )linked to Ktypes get integrated into the Amazon Part Finder? please help !