Need help to create Workflow on SharePoint Designer 2013

I've one list "Purchase Order" where I'm storing the data for purchase order details below are the fields.

List Name = Purchase Order Order No, Order Date, Part No, Part Qty, Delivery Date, Delivery Qty, Balance Qty.

Now in above list I'm storing the Purchase order details to check Order Qty and Balance Qty for every part no and this list is working fine.

Now my requirement is to create one more list to issue the Part No from available Balance Qty in above List "Purchase Order".

So I thought to create new list with below details (Please suggest me if you have other idea also I can use only SharePoint OutofBox feature or SharePoint Designer 2013):-

List Name = "Issue Order"

Issue No, Part No, Balance Qty, Issue Qty, Issue Date, Remaining Balance Qty OR Stock Qty

So in List Name "Issue Order" once user will select "Part No" the "Balance Qty" will show the available Qty (from Purchase Order List). And once he enter Qty in "Issue Qty" column it will show the remaining Qty in "Remaining Balance Qty OR Stock Qty" column.

Also "Remaining Balance Qty OR Stock Qty" will get update in "Balance Qty" column in first list "Purchase Order" list so next time when user will issue the Qty from "Issue Order" he will get the correct Qty for Part No.

Need your help to create workflow for List "Issue Order" so user can issue the items from this list and balance qty will update accordingly in List Name = Purchase Order. So next time when user will issue the "Part No" he will get correct quantity.