Officially divorced as of December 31, 2017? If you were divorced as of the end of 2017 then you can file as Single for 2017. You enter your filing status in My Info. You marital status is determined by the last day of the tax year--so if your divorce was not final until 2018 you cannot file as Single.
Do you have an account from last year year? Don't use it. Start your own new account and do not Transfer from last year. Online is only good for 1 return. But you can use the same email address for 5 accounts. How to start another return in the Online version https://ttlc.intuit.com/replies/3288574
Getting Divorced article
Video tips for Divorced couples