Working with two workbooks

[cristiander]

I'm working on a workbook that needs to make modifications on other workbooks, but I can't get the most rudimentary functions to work.
I think I might be defining my workbooks incorrectly.

As a start I have made:

Sub Work_tables()
    
    Dim tbl_a As Workbook
    Dim tbl_b As Workbook
    
    Set tbl_a = Workbooks.Open("C:\Users\...\table_a.xlsm")
    Set tbl_b = Workbooks.Open("C:\Users\...\table_b.xlsm")

    tbl_a.Sheets("sheet1").Range("A1").Value = 1
    tbl_b.Sheets("sheet1").Range("A1").Value = 2
    
    
End Sub

But it's simply not working. It's not changing any values. I don't understand where the problem is.
Is there something wrong with the definitions?

 

[cristiander]

Update:

I was using the macro in table_a, so instead of Set tbl_a = Workbooks.Open("C:\Users\...\table_a.xlsm") I needed to use Set tbl_a = ThisWorkbook