You must make a copy of your original return before you press the amend button.
Yes TurboTax will help you amend both the federal and state returns.
There are at least two videos I found using a search engine. They may not have as much detail as your looking for but I believe once to start the amendment you will get fairly detailed instructions for what to do.
https://turbotax.intuit.com/tax-tips/amend-return/video-how-to-amend-taxes-that-are-already-filed/L4...
https://turbotax.intuit.com/tax-tips/amend-return/video-how-to-amend-your-tax-return/L2wLEwRf1
