I didn't realize I was agreeing to the premium service. I only wanted the $29.99 service. How can I reverse it?

Have you already filed?   If you haven't filed yet, it can be removed.

Are you a California filer, and did you choose to pay the TurboTax product fees out of your Federal refund?   If so, that option to pay out of the refund is bundled with other benefits and called "Premium Services" for 39.99.

See this

FAQ:  What is the Premium Services Bundle?

https://ttlc.intuit.com/questions/2204687-what-is-the-premium-services-bundle 

If you want to, you can remove Premium Services prior to filing, and then choose to pay for your return with a credit card, debit card, or a prepaid debit card you can buy in a store. Here's how:

I didn't file once I saw the additional fee in the price. In the past I have never chosen the option of the fees to be deducted from my return. Now I fully understand that option comes with Premium Bundle along with that fee. Thank you for your insight.

You're welcome.  Good luck.

You were told exactly what you were signing up for and you agreed to it. There is no basis to reverse it.