Automatic Fill Question

Hey guys i'm new to the forum and I have a problem that I can't solve or seems to find solution online. Here I go:

So i have a large spreadsheet roughly about 6000 lines.
it looks like this
A B
7/1991 JFCOM
4/1992 JFCOM
8/1992 SOTHCOM
2/1993 JFCOM
..... ............

I want excel to automatically add X number of row to fill in the missing months and fill column B with the starting month. So i want it to look like this.

A B
7/1991 JFCOM
8/1991 JFCOM
9/1991 JFCOM
10/1991 JFCOM
11/1991 JFCOM
12/1991 JFCOM
1/1991 JFCOM
2/1991 JFCOM
3/1991 JFCOM
4/1992 JFCOM
....... JFCOM
8/1992 SOUTHCOM
....... SOUTHCOM
2/1993 JFCOM
........ JFCOM


Hope I explained it clearly and thank you in advance!

Try this macro

Sub Test()
For N = Cells(Rows.Count, 1).End(xlUp).Row To 2 Step -1
    If (Month(Cells(N, 1)) - 1 = Month(Cells(N - 1, 1)) And Year(Cells(N, 1)) = Year(Cells(N - 1, 1))) Then
    
    ElseIf (Month(Cells(N, 1)) = 1 And Year(Cells(N, 1)) - 1 = Year(Cells(N - 1, 1))) Then
        Rows(N).Insert
        Cells(N, 1) = DateValue(12 & "/" & Year(Cells(N - 1, 1)))
        Cells(N, 2) = Cells(N - 1, 2)
        N = N + 1
    Else
    
        Rows(N).Insert
        Cells(N, 1) = DateValue(Month(Cells(N + 1, 1) - 1) & "/" & Year(Cells(N + 1, 1)))
        Cells(N, 2) = Cells(N - 1, 2)
        N = N + 1
    
    End If
Next N
End Sub

Open up the VBA editor by hitting ALT F11

Insert a new module by hitting Insert - Module

Paste the macro into the empty sheet

Hit ALT F11 to get back to the worksheet.

Run the macro by going to tools-macro in Excel 2003 or the view ribbon in Excel 2007.