Assign activity to diferent Datatable (Syntax)

Hi everybody.
I am manipulating two cvs files because in cvs1 is missing some info that is in csv2 (nevertheless csv2 is BIG file with lot of columns).
I am reading cvs1 in variable DT1 and adding a columntable, that is OK.
I am reading cvs2 in variable DT2.
Then, For Each Row in DT1, I am filtering DT2 to get the missing info into a new variable DT3 (Note that inside FOR EACH I am using DT1. // I am using “for each” activity to pass on each row and search for the missin value//.
Now, I need to ASSIGN the filtered value (from DT3) TO DT1 new column. (using the Syntax: row(“column1”).ToString)
Here is the question:
How can I assign a row value (from DT3) if inside EACH ROW activity we are only refering to DT1. In the Syntax row (“name of the column”).ToString is implicity refering to DT1. I need to refer to DT3… (I tried DT3.rows(“name of column”).ToString without success.

I apreciate your time and suggestions.

Pass the unique reference that is common in both DT1 and DT3 to DT3 column to filter and get a single row. Then assign the column value to the record in DT1 as like below.

item.row("ColumnNameWanttoAdd") = DT3.row(0).item("ColumnName").ToString

Where item is the row variable in for each row activity