The default archive folder is a folder called Archive off the root folder (but it can be a user configured folder) . Assuming you have the default setup, the following should work.
Option Explicit
Sub ArchiveSelected()
'Graham Mayor - http://www.gmayor.com - Last updated - 12 Oct 2017
Dim olItem As Object
Dim olFolder As Outlook.Folder
Dim lngItem As Long
If Application.ActiveExplorer.Selection.Count = 0 Then
MsgBox "No Items selected!", vbCritical, "Error"
Exit Sub
End If
On Error Resume Next
Set olFolder = Session.GetDefaultFolder(olFolderInbox).Parent.folders("Archive")
'Process each selected message
For lngItem = Application.ActiveExplorer.Selection.Count To 1 Step -1
Set olItem = Application.ActiveExplorer.Selection(lngItem)
olItem.UnRead = False
olItem.Move olFolder
Next lngItem
lbl_Exit:
Set olItem = Nothing
Set olFolder = Nothing
Exit Sub
End Sub