Do you need to purchase the 2018 version of TurboTax Business?
If so, you can purchase it via this link --> https://turbotax.intuit.com/personal-taxes/past-years-products/
If you need to re-download the software, you can sign in to your Intuit account to do so.
https://accounts.intuit.com/index.html?offering_id=Intuit.platform.commercewidgets.checkoutexperience&redirect_url=https://shopping.turbotax.intuit.com/app/downloads