If you are using TurboTax CD/Download- You will need to click on Easy Steps and then enter your marital status as "Single" and complete the page then click on next and go back to Forms.
If you are using TurboTax Online and have forwarded your information from 2018 into your 2019 return and have changed your marital status - "Single" would not be an option if the year previous you had a different marital status.
https://turbotax.community.intuit.ca/community/navigating-turbotax/help/why-won-t-turbotax-let-me-ch...
