There is no amended PTCX form. If you need to make corrections to what was filed, You will file a 1040XN and include a corrected Form PTC.
To amend the state return but not the federal you will use the "Add a state" option when signing in to your TurboTax account. This will allow you to make changes to your return without initiating a federal amendment.
Once you are back in the return go to your state interview and click through to the page asking if you want to amend your state return. Click "Yes" and follow the prompts to complete the state amendment. In the end, you will get the printing/mailing option for the state amendment.