This option is available in the premium version of the plugin.
This advanced option gives you the power of specifying your own labels for the filtering parameters that appear in the URL string of the filtered page address. For example, if you wish to change the auto-generated “pa_sizes-filter” URL parameter to “sizes”, set it as the parameter label for the product sizes attribute. This will result in your filtered URL being transformed from www.yourshop.com/?pa_sizes-filter=s,m,l to www.yourshop.com/?sizes=s,m,l.
Be careful not to assign the parameter names that are reserved by the WordPress itself, WooCommerce, or any of the plugins that are running on your site. Doing so may result in errors and unpredictable filters behavior.