Combining Subtotal, if, left right etc with filter

[akenb]

Hi,
I have a list of "Customers" in column A (A2-A270) in my first tab.
In columns B-G (listing "Item name" in B1-G1) I have listed a year slash a number: e.g. 2018/1000 (years ranging from 2017-2020.
What I want to do is to be able to form a table per customer in a secondtab depending on which customer is visible after filtering in my first tab.

Tab 1:

	Item1	Item2	Item3
Customer 1	2017/2000	2018/890
Customer 2		2020/8950	2017/780
Customer 3	2018/5000

<tbody>
</tbody>

This table in tab2 I want to have like this:
Items on rows, years in columns and in the cells in between I want to list the number given in column B-G in my first tab.

Customer 1 chosen with filter in tab1 -->
Tab2:

	2017	2018	2019	2020
Item 1	2000
Item 2		890
Item 3

<tbody>
</tbody>

I have the following formula but it doesn't take the filtering in tab 1 into consideration. How can I do this?
=IF(VALUE(LEFT(Tab1!B2;4))=Tab2!B1;VALUE(RIGHT(Tab1!B2;(LEN(Tab1!B2)-5)));0)
if
Tab1!B2= statement for item 1 customer 1
Tab2!B1= year in table in Tab2

I know you can use the formula subtotal for filtered values - but how do I integrate if, left, right formulas etc.?
It is okay that the table in Tab2 only works when there is only one customer visible in filter i Tab1.

Thank you.