You must file separate tax returns for 2017 and 2018 and only include information for each year on each tax return. You can use the current online products to prepare and file a 2018 tax return. You must buy and download to your computer the 2017 product to file a 2017 tax return. Here is where to buy it: https://turbotax.intuit.com/personal-taxes/past-years-products/
If you will have anything on your 2017 tax return that might carry forward to 2018, you should do your 2017 tax return first and then transfer from your 2017 return to your 2018 return when you first start it.