Business is sole proprietorship and closed the business last year Sept and when we did the return for 2016 we forgot to show this was the final return.
Do we amend the 2016 return? Thanks

No.you do not have to; There is no requirement to inform the IRS about the closing of your sole proprietorship. Your final Sch C does not have to include any kind of notification. So, it is not necessary that you write "Final Return", or any other comment on Sch C. Simply fill out your final Sch C as if the business was still active. If your business was inactive for the entire year, it is not necessary to file Sch C. Your business is considered inactive if it had neither incomenor expenses for the entire year