The idea here is two columns and when data is in column B there is a blank in Column A and you want to combine the two columns.
Dim rcell As Range, rng As Range
Dim ws As Worksheet
Set ws = ThisWorkbook.Sheets("Sheet1")
Set rng = ws.Range("A1:A" & Application.ActiveSheet.UsedRange.Rows.Count)
For Each rcell In rng.Cells
If IsEmpty(rcell.Value) = True Then
rcell.Value = rcell.Offset(0, 1).Value