I forgot to put business expenses on my tax return that I already filed. What do I do?

If you need to add to your tax return you have already filed, you will need to amend your tax return.  

This article gives instructions for amending a tax return. If you used TurboTax Online, simply log in to your account and select “Amend a return that was filed and accepted.”

Some business expenses you took last year might not qualify as an expense this year due to tax reform.  

This article on tax reform might help you determine whether the expenses you are talking about will be deductible.

I also forgot to put that I didn't have income for the business. It never opened.