I have some free time, so I wrote this code for you below. However, it's best to always show your efforts when positing questions. Usually people don't just write code for you.
Sub FillBlanks()
Dim wks1 As Worksheet, wks2 As Worksheet
Set wks1 = Sheets(1) 'change to your needs; could also be Sheets("Sheet1") format
Set wks2 = Sheets(2) 'change to your needs; could also be Sheets("Sheet1") format
Dim rngLookup As Range
'assume data on sheet2 is on column A
With wk2
Set rngLookup = .Range(.Range("A1"), .Range("A" & .Rows.Count).End(xlUp))
End With
With wks1
Dim rngSearch As Range
'assume blank cells are in column A on sheet 1
Set rngSearch = .Range(.Range("A1"), .Range("A" & .Rows.Count).End(xlUp))
Set rngSearch = rngSearch.SpecialCells(xlCellTypeBlanks)
Dim cel As Range, i As Integer
i = 1
For Each cel In rngSearch
cel.Value = rngLookup.Cells(i, 1)
If i = rngLookup.Rows.Count Then i = 1 Else: i = i + 1
Next
End With
End Sub