I already started my TurboTax but noticed on my Fidelity Portfolio page that they have a link offering Turbo tax premium for free. Can I still take advantage of that?

Sorry, you have to start your tax return from the Fidelity link to TurboTax to get the offer. 

How do I start over?  When I click on the Fidelity Turbo Tax link it takes me to my existing Turbo Tax account and wants me to "continue where I left off"  .   I would like to start over and take advantage of the savings

If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return and start over. Click on Tax Tools on the left side of the program screen while working on the 2023 online tax return. Click on Clear & Start Over.