Now go to the Visual Basic in Developer Tab.
Double click on This workbook and paste the below vbu code.
Private Sub Workbook_Open()
'Sub FillEmptyBlankCellWithValue()
Dim cell As Range
Dim InputValue As String
On Error Resume Next
InputValue = InputBox("Enter value that will fill empty cells in selection", _
"Fill Empty Cells")
For Each cell In Selection
If IsEmpty(cell) Then
cell.Value = InputValue
End If
Next
End Sub
Now click this to check whether its working or not.
Remember to save your file as Micro enable format in .xlsm format.
All set!!
Sample Add Zero in Blank Cell