Please see this FAQ on how to enter a backdoor Roth Conversion:
https://ttlc.intuit.com/replies/6768029
When you enter your traditional IRA contribution make sure you make it nondeductible and only enter the contribution for 2018.
After entering your 1099-R please ensure that you click "continue" after the "Your 1099-R Entries" screen and answer "yes" to "Any nondeductible Contribution to your IRA?" Then on the next screens, you will need to answer the questions about the basis.