1. Filtering is core part of prestashop, it is module ps_facatedsearch in which you need to configure filter template

2. If you configured filter template and it is visible but not working it is very possible that it is doubled(displayed twice) so then please

• go to themeditor > content > product list > and disable facated search above product list
• OR  unhook ps_facatedsearch module from displayLeftColumn in backoffice > design > positions or set full width layout for category pages http://iqit-commerce.com/xdocs/warehouse-theme-documentation/#layoutscolumns