Two words of 3 letters twice

A solution with Regular Expression

Sub jec()
 Dim ar, j As Long, y As Long
 ar = Range("a1").CurrentRegion
 ReDim ary(UBound(ar), 0)
 
 With CreateObject("VBScript.RegExp")
   .Global = True
   .Pattern = "([A-Z]{3})(?=.*?\1.*$)"
    For j = 1 To UBound(ar)
       If .test(ar(j, 1)) Then
         ary(y, 0) = ar(j, 1)
         y = y + 1
       End If
    Next
    Range("G1").Resize(y) = ary
 End With
End Sub