Add AST tracking info in customer SMS using Twilio SMS Notifications plugin

wc_twilio_sms_compatibility.php

/* add AST tracking info in customer SMS using Twilio SMS Notifications plugin */
add_filter( 'wc_twilio_sms_customer_sms_before_variable_replace', 'ast_pro_wc_twilio_sms_message_replacement', 10, 2 );

if ( !function_exists( 'ast_pro_wc_twilio_sms_message_replacement' ) ) {
	function ast_pro_wc_twilio_sms_message_replacement( $message, $order ) {	
		
		if ( !function_exists( 'ast_get_tracking_items' ) ) {
			return;
		}	
		
		$order_id = $order->get_id();		
		
		$order_status = $order->get_status();
		
		$tracking_items = ast_get_tracking_items($order_id);
		
		//echo '<pre>';print_r($tracking_items);echo '</pre>';
				
		//You can comment this condition if you don't want to add tracking information on completed order status SMS message.
		if ( 'completed' == $order_status || 'shipped' == $order_status ) {
			if ( count( $tracking_items ) > 0 ) {
				foreach ( $tracking_items as $key => $tracking_item ) {	
					$message .= sprintf( __( "Your order was shipped with %s and your tracking code is: %s", 'ast-pro' ), $tracking_item['formatted_tracking_provider'], $tracking_item['tracking_number'] );		
				}
			}			
		}
		
		//You can comment this condition if you don't want to add tracking information on Partially Shipped order status SMS message.
		if ( 'partial-shipped' == $order_status ) {
			if ( count( $tracking_items ) > 0 ) {
				foreach ( $tracking_items as $key => $tracking_item ) {	
					$message .= sprintf( __( "Your order was Partially Shipped with %s and your tracking code is: %s", 'ast-pro' ), $tracking_item['formatted_tracking_provider'], $tracking_item['tracking_number'] );		
				}
			}			
		}	
		
		return $message;
	}
}

Where do you add this?