How to refer to the workbook where the macro when another workbook is open during runtime?

[jonelamora]

Basically I have 2 workbooks open at the same time say (WS and WB)
WS<--- where the macro is
WB<--- a workbook opened during runtime

during runtime WB is activated to check for comparisons and if the values are not
equal I need to write something on WS for the log and then continue the check on WB.
how do I do this?

I tried

thisworkbook.sheets("log").range("A1").value = "something"

but it results to error.
Any help would be greatly appreciated thank you!