Add Custome Price in wocommerce Plugin

Hello,

I am creating site using wocommerce plugin of wordpress.

I want to change my product price for only particular users.
It will same for all which we provide in product detail.
But when for only few user add this product into cart ,the price will be change as per my requirement.

I found some code for that , but don’t know how can I use that and where I put that modification.

add_action( 'woocommerce_before_calculate_totals', 'add_custom_price' );
                function add_custom_price( $cart_object ) {
                        $custom_price = 50; // This will be your custome price
                        foreach ( $cart_object->cart_contents as $key => $value ) {
                            $value['data']->price = $custom_price;
                    }
                }

Any one can help me. It’s urgent for me.

Thanks
Crish