Combine 2 tables together

I have 2 tables, where material number is merged.

Table1:

Table2:

When I created variable field "Kg", where Quantity from table1 * Weight from table2 divide 1000 and insert in the table2 field "Kg", work fine! But in table2 I need insert additional field from table1 "Supplier", when I insert I get error.

What is correct way, that I can insert supplier in Table2?