VBA Calculates Sum If From CSV Workbook

Sample stock system LOADTESTING.xlsm has ten products. "LoadTesting" shows the opening stock for each. CSV file "Van Sales" has the Stock Number in Col M and the sales figure in Col N. I want the code to Open a CSV file "Van Sales" (which for some reason the site would not upload) Establish the sum total sold for each product (VBA equivalent of SUMIF) Deduct that sum for each item from the opening numbers on "Van Sales" (e.g. Product 001 started with 156 on the van, 92 were sold, so the "revised" van figure should be 64).

Can't get the code to link to the right "ranges" from the Van Sales workbook.

(You will have to change the file path calling the Van Sales file, but if you do get it to work,

VB:
Option Explicit
Sub GETSALE()
Dim Dest As Range, Dest1 As Range, Dest2 As Range, Dest3 As Range, oCell As Range, varResult As Variant

[Code].....