Inverted structure

one of my client has accumulated itc
due to reduce in gst return.
he wants to claim itc under inverted structure scheme.
he has stock of goods purchased at 28% and subsequently due to reduce in gst rate he has sale the same @ 18%. in this case what will be the adjusted total turnover. does it includes the goods Sale 28% or only the Sale @ 18%.
and what will be the net ITC. do I need to take the purchased at 18% or just purchased at 28%.