Macro to switch two cells value

I need macro that will basically store contents of cell once selected and on next selection store contents of that cell then paste the cell info from first selected cell into the second selected cell and the info from the second selected cell into the first then turn this feature off until active again

Coding so far

Public Bt_On As String

Sub Bt1()
Bt_On = "Yes"
End Sub


Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim x As Range, y As Range
Dim tmp1 As String, tmp2 As String
If Bt_On = "Yes" Then
x = Target.Address
tmp1 = x.Value

'Not sure what to put to make it work on next selection

Bt_On = ""
End If

End Sub

edit: fix code brackets