Based on your example, this will format the word "Excel" in bold red font if it is found in the text of any comments on the active sheet. You can modify the term from "Excel" to something else in the code by changing this line
TextToFormat = "Excel"
to some other term.
Sub Test1()
Application.ScreenUpdating = False
Dim cell As Range, i As Integer
Dim cText As String, TextToFormat As String
TextToFormat = "Excel"
On Error Resume Next
For Each cell In Cells.SpecialCells(1)
cText = cell.Comment.Text
If InStr(cText, TextToFormat) > 0 Then
With cell.Comment.Shape.TextFrame
.Characters.Font.Bold = False
.Characters.Font.ColorIndex = 1
For i = 1 To Len(cText) - Len(TextToFormat) Step 1
If Mid(cText, i, Len(TextToFormat)) = TextToFormat Then
.Characters(i, Len(TextToFormat)).Font.Bold = True
.Characters(i, Len(TextToFormat)).Font.ColorIndex = 3
End If
Next i
End With
If Right(cText, Len(TextToFormat)) = TextToFormat Then
With cell.Comment.Shape.TextFrame.Characters((Len(cText) - Len(TextToFormat)), Len(cText)).Font
.ColorIndex = 3
.Bold = True
End With
End If
End If
Next cell
Application.ScreenUpdating = True
If Err.Number <> 0 Then
Err.Clear
Application.ScreenUpdating = True
MsgBox "No cells on this sheet contain comments.", 48, "Nothing to format."
End If
End Sub