Your prior returns filed with TurboTax Online, will be in the Tax Returns and Documents section of your account. Read below for additional information on accessing your 2017 return. https://ttlc.intuit.com/replies/5574744
If you're still not able to locate your tax returns, it could be that you have another account linked to your email address, and you filed your returns with this other account. Use the FAQ below to find out how to locate other accounts linked to your email address. https://ttlc.intuit.com/replies/3302270