Changing inventory in shopify using formulas!

Hey Team!

Here is what I am trying to do.
I have 4000 skus that I need to change the inventory for. I have a file that has the proper inventory numbers but it isnt in order.
There are also some on each list that are unique to that list.

So I need to have a cell find its match and if it does find its match, change the value of another cell to match another cell.
I know thats confusing but here is what it could look like.

=IF(A1=B1)>C1=D1.

I know that is way off and not nearly correct.

Any help would be greatly appreciated.