If you purchased audit support when you filed, you should contact them.
It's not clear what change was made, and whether it was your own mistake or you are thinking that Turbotax made a mistake. If it was your mistake, and you agree with the bill, you can just pay it. You don't need to file an amended return as the state has already adjusted your account (unless the letter specifically instructs you to prepare an amended return).
If it was your mistake but you disagree with the final tax amount, you may want to prepare an amended return to see what the correct tax would be. If you can show that your original return was wrong, but the recalculation was also wrong, and the amount you owe is less, you may be able to appeal the determination. How to do this and what the deadlines are depends on your state, and the information should be in your letter.
If you believe Turbotax made a mistake, you always owe your own correct tax, but Turbotax is responsible for any interest and penalties (if it was truly a program error). You should pay the bill now (to prevent the interest and penalties from growing even larger) but then you can file a claim on the accuracy guarantee. You must do this within 30 days of getting the deficiency notice.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/account-management/turbotax-100-accurate...
