You mean you want to add custom filter to search engine portal. That is, faceted search. Then follow these steps to add faceted search to the portal you use.
Out-of-the-box faceted search is enabled in your portals. To control or enable it, follow these steps:
Open the Portal Management app and go to Portals > Website > Site Settings.
Select the Search/FacetedView site setting.
Change the Value to True to enable or False to disable faceted search.
To disable a single piece of the faceted view:
Open the Portal Management app and go to Portals > Web Templates.
Select the view to disable (that is, Knowledge Management – Top Rated Articles)
Select Deactivate at the top of the page.
Regards.