How to add a number from a form to a table cell?

Question

Google Apps Script

There is a table warehouse Googgle Spreadsheets and a form for issuing goods. In the form, select a product, N - how many pieces we get. N must be added to the cell with the quantity of goods.
Link to the table (you can comment)
Link to the form
As I understand it, you need a script that, at the time of submitting the form, will find the product in the table and add a variable. Or pick up the number from the responses to the form and process it using the table.
I myself have never been a programmer, I will be glad for any of your help.

Answer 1

So far, I've gone around like this: there is a warehouse, a list is made from the tool in the form, a pivot table is formed from the answers to the form, the same answers are summed up, the quantity goes back to the warehouse, then to the budget.
warehouse -> form -> form responses -> pivot table -> warehouse -> budget
pluses:
It works
minuses:
If you change the name of the product, the responses to the form will contain both old and new names, the pivot table will become one line more and everything in the warehouse will float one line down. To notice copies in responses to the form added data validation.