I need to reformat my Vlookup formula in excel - vba

Question

I have a VBA code as you can see below, I recorded it. While recording it, it wrote the formula in offset format. So I don't know how to change the range
How can I convert;
R3C[-3]:R[1488]C[2] which is normally B$3:G1489
to:
B$3:(last active cell in column "G")
How can I do that?
Sub duzenle()
Columns("E:E").Select
Selection.Copy
Range("L1").Select
ActiveSheet.Paste
Range("E12").Select
Application.CutCopyMode = False
ActiveCell.FormulaR1C1 = _
"=IFERROR(VLOOKUP(RC[-3],C.A.!R3C[-3]:R[1488]C[2],4,0),IF(ISBLANK('2017'!RC[7]),"""",'2017'!RC[7]))"
Range("E12").Select
Selection.AutoFill Destination:=Range(ActiveCell, ActiveCell.End(xlDown)), Type:=xlFillDefault
Range(ActiveCell, ActiveCell.End(xlDown)).Select
Columns("E:E").Select
Selection.Copy
Range("E1").Select
ActiveSheet.Paste
Selection.PasteSpecial Paste:=xlValues, Operation:=xlNone, SkipBlanks:= _
False, Transpose:=False
Columns("L:L").Select
Application.CutCopyMode = False
Selection.Delete Shift:=xlToLeft
Range("A1").Select
MsgBox "'C.A' Degerleri Guncellenmistir."
End Sub

Answer 1

You can remove some of your unnecessary Select, Selection and by replacing the first few code lines of yours:
Columns("E:E").Select
Selection.Copy
Range("L1").Select
ActiveSheet.Paste
With:
Columns("E:E").Copy Range("L1")
Regarding your formula, you need to replace FormulaR1C1 with Formula, see code below:
With Worksheets("C.A.")
LastRow = .Cells(.Rows.Count, "G").End(xlUp).Row '<--get last row with data in Column G from "C.A." sheet
End With
Range("E12").Formula = _
"=IFERROR(VLOOKUP(B3,C.A.!B$3:G" & LastRow & ",4,0)...' <-- the rest of your formula
Edit 1: just corrected the Formula code line:
Range("E12").Formula = "=IFERROR(VLOOKUP(B3,C.A.!B$3:G" & LastRow & ",4,0),IF(ISBLANK('2017'!L12)," & Chr(34) & Chr(34) & ",'2017'!L12))"