Hello David, thank you for your response.
I'm able to import the SKP file in to the User Catalog. However, I am facing an issue while trying to assign it from "Edit - Default Settings - Cabinet - Door/Drawer tab". When I try to select a new handle from the Library, the content is filtered by "Hardware". Unfortunately, I am unable to unfilter the content, which is why my SKP file is not showing up. It appears that external 3D symbols are being imported as "Fixtures Interior". I tried changing the category of my symbol to hardware by editing the Components section to ID: Hardware, but it still does not recognize it as hardware.
Thank you!