You do not have to file a 2018 return if you did file a 2019.
These links may help explain and guide you through the process.
https://turbotax.intuit.com/stimulus-check/ link to stimulus registration (SR). It is very important that you uses this link that says register now if you don't need to file taxes this year. Otherwise, you will not be able to E-file a zero return. It also has the calculator.
The IRS says it is working on developing a web-based system for people to give the government their direct-deposit information. Keep checking www.irs.gov/coronavirus for more details on this.