Sounds like you still need to file your 2017 return - you can't do this in the online product, you'll need to purchase the 2017 desktop product. Since you filed 2018 with your 2017 information, you'll need to file an amended return for 2018. You can do this online, but you'll probably want to call us for assistance in walking through the process. More information is available below.
https://ttlc.intuit.com/replies/3288565