In turbotax 2018, how do I enter my form 5498 ira contribution to add to my ira basis if I did not get a 1099-r form?

What type of contribution?    Roth or Traditional IRA?
Was it a 2017 contribution made in 2018 or a 2018 contribution?

Form 5498 is an "informational" form and does not need to be entered.  That said, you do need to track the basis of your Roth IRA.  To enter your Roth contribution, type "Roth IRA" in to Search, and hit enter.  Then click on "Jump to IRA".  Continue with the interview.