Code:
Sub Macro1()
Dim oRng As Word.Range
Selection.Find.ClearFormatting
Selection.Find.Replacement.ClearFormatting
Set oRng = ActiveDocument.Range
With oRng.Find 'Selection.Find
.Text = "([0-9]{1,})(:)([0-9]{1,})"
.Replacement.Text = "\3\2\1"
.Forward = True
.Wrap = wdFindContinue
.Format = False
.MatchCase = False
.MatchWholeWord = False
.MatchAllWordForms = False
.MatchSoundsLike = False
.MatchWildcards = True
.Execute Replace:=wdReplaceAll
End With
End Sub