You can use Clear and Start Over" as long as you haven't yet paid or registered the product. See this video for an overview, and then below I tell you 2 things that may hide the Tax Tools tab.
FAQ: How do I clear and start over?
There are 2 reasons you may not be seeing TAX TOOLS in the left column menu.
If your return interview is open, you will have a full left-column menu, but the bottom part of it may be hidden by the overlapping lower portion. The top portion of the left menu scrolls up and down separately from a bottom portion. It's possible for part of the menu to be hidden behind the bottom part of the menu. So try scrolling the top part of the menu to bring TAX TOOLS up higher and into view.
The other possibility is that you could have an incomplete left column menu due to your return not being open. The return has to be open to have a full left-column menu. It you can get back inside your return interview, do that before trying to go to TAX TOOLS. If TurboTax thinks you were finished, however, it may have closed your interview. If that's the case, then at the Tax Home look for a link "Add a State" to reopen the interview. (That doesn't really add one.)