I don't see that being very useful.
It tells me what your Cells look like and it tells me how to set the subscript Font size.
Off the top of my head, not compiled, not tested
Sub SamT()
Dim YourRange as Range
Dim Cel As Range
Dim i as Long
Dim j As Long
Set YourRange = ???
For each Cel in YourRange
For i = Len(cel) to 1 Step -1
'Check backwards to first non-Subscript
If Mid(Cell, i, 1).Font.Subscript = False then
If i = Len(Cel) then 'The last character is non-Subscript, check next cel
GoTo CelNext
Else 'The first non-subscript is not the last character
J = i + 1 'Start of Subscript
With Right(Cel, j).Font
.Size = 20
.Subscript = true
End with
End if
End If
Next i
CelNext:
Next Cel