Application_Reminder is a built-in function. There can only be one and it goes in the ThisOutlookSession module.
You can use it to call other macros in other folders based on the conditions you are looking for in the message to determine what happens. e.g. You could test for the subject as below or for some other variable criteria and run a different macro based on the result.

 
Private Sub Application_Reminder(ByVal Item As Object)'Updated by Extendoffice 20200522
Dim xMailItem As MailItem
Dim xItemDoc As Word.document
Dim xNewDoc As Word.document
Dim xFldPath As String
    On Error Resume Next
    If Item.Class <> OlObjectClass.olAppointment Then Exit Sub
    If Item.Categories <> "Send Schedule Recurring Email" Then Exit Sub


    Select Case Item.Subject
        Case "Subject 1"
            Call Reminder1(Item)
            Exit Sub
        Case "Subject 2"
            Call Reminder2(Item)
            Exit Sub
        Case "Subject 3"
            Call Reminder3(Item)
            Exit Sub
    End Select
    'Not one of the above so run the erst of the code below


    Set xMailItem = Outlook.Application.CreateItem(olMailItem)
    Set xItemDoc = Item.GetInspector.WordEditor
    xFldPath = CStr(Environ("USERPROFILE"))
    xFldPath = xFldPath & "\MyReminder"
    If Dir(xFldPath, vbDirectory) = "" Then
        MkDir xFldPath
    End If
    xFldPath = xFldPath & "\AppointmentBody.xml"
    xItemDoc.SaveAs2 xFldPath, wdFormatXMLDocument    ' wdFormatXML
    Set xNewDoc = xMailItem.GetInspector.WordEditor
    VBA.DoEvents
    xNewDoc.Application.Selection.HomeKey
    xNewDoc.Activate
    xNewDoc.Application.Selection.InsertFile FileName:=xFldPath, Attachment:=False
    With xMailItem
        .To = Item.Location
        .Recipients.ResolveAll
        .Subject = Item.Subject
        .Attachments.Add "XXX\XXX\XXX\XXX.doc"
        .Send
    End With
    Set xMailItem = Nothing
    VBA.Kill xFldPath
End Sub


Sub Reminder1(ByVal Item As Object)
MsgBox "Reminder1"
End Sub


Sub Reminder2(ByVal Item As Object)
MsgBox "Reminder2"
End Sub


Sub Reminder3(ByVal Item As Object)
    MsgBox "Reminder3"
End Sub