spryker get data from sales_order_item table by passing id_sales_order_item value in TriggerMerchantOmsController

Question

I am new to spryker and I want to do some calculation when merchant ships an order, for that I have extended TriggerMerchantOmsController.php file and tried to get data from spy_sales_order_item but I couldn't, Can anyone help on how to get the data