vba/code to bring up msg box when critaria is met that contains data from comment box

I've written a function that works with this alteration in Column H:

=_xlfn.IFERROR(IF($A2="","",GetComment(MATCH($A2,'COMBINED MEMBERS'!$A$1:$K$11700,0))),"NOT FOUND")

Function GetComment(r As Long) As String: Dim C As Range, T As Comment 'XWarlock
Dim wc As Worksheet, ws As Worksheet, S As String
Set wc = ActiveWorkbook.Worksheets("COMBINED MEMBERS")
Set ws = ActiveWorkbook.Worksheets("BLANK SIGN IN SHEET")
For Each C In wc.Range("A" & r & ":C" & r)
If Not C.Comment Is Nothing Then
Set T = C.Comment
S = T.text: S = Mid(S, InStr(1, S, ":") + 1, Len(S))
S = Right(S, Len(S) - 1): S = Left(S, Len(S) - 1)
Exit For: End If: Next
GetComment = S
End Function

It's not a pop up and may not be what you want.