Plugins – Overwrite WP Class Private Function

I'm new to the community. I think you can help me with that.
I have plugin installed and I want to override a function that is in the class

            if( !empty( $role_ok ) ){
                $user_ok = true;
        return $user_ok;

I would like to rewrite if this is the case. WP uses my custom plugin instead of the plugin
I need a single change in the new function (I mean, I just need to pass "Subscriber" in array)

$wf_roles = apply_filters( 'wf_user_permission_roles', array('administrator', 'shop_manager', 'subscriber') );