Thank you all, for your proactive suggestions. I could solve it taking reference to your ideas.
Solved program is like this

Sub FiRe()
Application.ScreenUpdating = False
Dim Tbl As Table, FndList, RepList, i As Long
FndList = Array(ChrW(257), ChrW(275), ChrW(299), ChrW(333), ChrW(363))
RepList = Array("A", "E", "I", "O", "U")
Selection.HomeKey Unit:=wdStory
With ActiveDocument

With Selection.Find
For i = 0 To UBound(FndList)
.Text = FndList(i)
.Replacement.Text = RepList(i)
.Execute Replace:=wdReplaceAll
Next
End With


Application.ScreenUpdating = True
End With

End Sub

Thank you all once again