Return Order: Add Quantity to Stock

Hi,

I need a custom work done.

Functional specification:
When a customer returns a product using Opencart's standard return feature, from admin interface we can see Sales -> Returns. I'd want to have the functionality to press a button and return the stock quantity back to the product and change the return status to complete.

Technical specification:
1) At Sales -> Returns page, for the table listing, add a button in Action column beside blue pencil edit button. When press this button, get RETURN-MODEL, RETURN-QUANTITY and update PRODUCT-QUANTITY (PRODUCT-QUANTITY = PRODUCT-QUANTITY + RETURN-QUANTITY). Change return status to complete.
* I know it's better to use RETURN-PRODUCT_ID but I think there's a bug in Opencart 2.3.0.2. This field is never updated.
* Anywhere else we need to update the product quantity?

2) At Sales -> Returns page, after we click the edit button, we will see "Edit Product Return" page, to the left of the save button, add a button to have the functionality to add quantity back to stock, same as above and change return status to complete.

Custom modification required for Opencart V2.3.0.2.

Please provide costing and man days. Thank you.