This is easier said than done as there is no correlation between the two messages.
They will presumably have the same original subject in the body text and they may have the same time of sending of the original message and they should have the same original sender, but there are many areas where this could go wrong and either no message is flagged or the wrong message is flagged.
The following may work, but much depends on how your mail system is configured and what is actually in the messages, but if not you may be able to alter it to suit.
It assumes that the messages sent directly to you, and are to be categorised, are in the default Inbox. I have included a test macro to test the premise with a message received from your manager that also exists in your inbox. If it works run the main script from a rule that identifies messages from your manager.
Code:
Option Explicit
Sub Test()
Dim olMsg As MailItem
On Error Resume Next
Set olMsg = ActiveExplorer.Selection.Item(1)
FlagMessage olMsg
lbl_Exit:
Exit Sub
End Sub
Sub FlagMessage(olItem As MailItem)
Dim strName As String
Dim strSubject As String
Dim strTime As String
Dim vItem As Variant
Dim vText As Variant
Dim vSubject As Variant
Dim i As Long
Dim olFolder As Folder
Dim olItems As Items
Dim olMsg As MailItem
With olItem
If LCase(.Subject) = "for examination" Then
vText = Split(olItem.Body, Chr(13))
For i = 0 To UBound(vText)
If InStr(1, vText(i), "From: ") > 0 Then
vItem = Split(vText(i), Chr(58))
strName = LCase(Trim(vItem(1)))
strName = Replace(strName, " [mailto", "")
Exit For
End If
Next i
For i = 0 To UBound(vText)
If InStr(1, vText(i), "Sent: ") > 0 Then
vItem = Split(vText(i), Chr(58))
strTime = Trim(vItem(1)) & Chr(58) & vItem(2)
Exit For
End If
Next i
For i = 0 To UBound(vText)
If InStr(1, vText(i), "Subject: ") > 0 Then
vItem = Split(vText(i), Chr(58))
strSubject = LCase(Trim(vItem(UBound(vItem))))
Exit For
End If
Next i
Set olFolder = Session.GetDefaultFolder(olFolderInbox) 'the folder where the messages are stored
Set olItems = olFolder.Items
olItems.Sort "[Received]", True
For i = 1 To olItems.Count
Set olMsg = olItems(i)
If Format(olMsg.ReceivedTime, "dd mmmm yyyy HH:MM") = strTime Then
vSubject = Split(LCase(olMsg.Subject), Chr(58))
If strSubject = Trim(LCase(vSubject(UBound(vSubject)))) And _
strName = LCase(olMsg.Sender.Name) Then
olMsg.Categories = "Worked"
olMsg.Save
Exit For
End If
End If
Next i
End If
End With
lbl_Exit:
Set olFolder = Nothing
Set olItems = Nothing
Set olMsg = Nothing
Exit Sub
End Sub