Couple of ways to do this, but without knowing much more what about
If DLookup("[Prioryte]", "tblZlecenia ", "[ID_Zlecenia]=" & Me.Lista0) <> 7 Then
Msgbox "This is Not 7"
END IF
of course you can replace
Msgbox "This is Not 7"
With your update code
try it on the AfterUpdate Event of the...