I cannot figure out how to do a 1040X using TurboTax Premiere. Shouldn't I start by using my original filing? Is there a way to move to an amended return from there?

After the TurboTax online tax return has been completed and filed you can amend the return.

Before starting to amend the tax return, wait for the tax refund to be received or the taxes due to be paid and processed by the IRS.

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-already-filed/L4VjJ9BA2_US_en_US?uid=ld1n99kr

And---before you amend, make sure you save a pdf of the original tax return.   If you do not do that, you will lose the original return, because the amended return will replace it in the software.