Where do I add the code for redirect after registration?

Hi,

I am new to this, so probably a silly question. I want to redirect to the page a user was on before registration. I found this code

add_action( 'user_registration_before_customer_login_form', 'ur_set_redirect_url' );
function ur_set_redirect_url() {
if ( isset( $_SERVER['HTTP_REFERER'] ) ) {
set_transient( 'originalLoginRefererURL', $_SERVER['HTTP_REFERER'], 60 * 60 * 24 );
}
}
add_filter( 'user_registration_login_redirect', 'ur_redirect_back', 10, 2 );
function ur_redirect_back( $redirect, $user ) {
if ( true === ( $redirect_url = get_transient( 'originalLoginRefererURL' ) ) ) {
delete_transient( 'originalLoginRefererURL' );
return $redirect_url;
}
return $redirect_url;
}

Where do I add this code for this to work?

Thanks