Need help writing a better loop

I need to find a better way to write the code below. The code below works great, but then it's looping through my whole data in order to accomplish what I want. The thing is my data can have 40,000 rows and it's taking forever. Is there a better way to write this?

Basically, what the code below doing is looping through my data and evaluate the data in column D and G. If they are both "CONTRACT" and "ABC COMPANY". If that's the case, it will change the value in column D, which is "CONTRACT" to "CONTRACT ENG".


I think another way to write the code is to do an autofilter and filer column D and G by "CONTRACT" and "ABC COMPANY". Once it's filtered, it would only be less than 20 rows of data that match that criteria. I can loop through those 20 rows, it's much faster than have the macros loop through 40k rows. I just don't know how to do it. Can someone help me?

Last_Row = Cells(Rows.Count, "D").End(xlUp).Row

Range("D2").Activate

For I = 2 To Last_Row

If ActiveCell.Value = "CONTRACT" And ActiveCell.Offset(0, 3) <> "ABC COMPANY" Then

ActiveCell.Value = "CONTRACT ENG"


ActiveCell.Offset(1, 0).Activate

Else

ActiveCell.Offset(1, 0).Activate

End If

Next I