Ok ... did you file the original state return by mail already?
If so was it fully processed and did you get the original refund or pay the original balance due ?
If so you will start the amendment process and then skip the federal section if you only have to amend something in the state section ... be aware that many things that affect the state originate in the federal section.
See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
