In the eyes of the IRS, you are considered self-employed if you received a Form 1099-NEC for services performed by you. So, TurboTax is on the right track.
This means that you do need to include a Schedule C as part of your amended return to report your self-employment income and any associated expenses. You are not required to have a Federal ID number for Schedule C if that is the business ID you are referring to in your question (as also confirmed by Critter-3). You will need to specify the type of work that you did so that a business code can be entered on Schedule C.
Once you start through the process of amending your return, you will need to add Schedule C and Form 1099-NEC. The following TurboTax help article will guide you through that process:
How do I report income from self-employment?
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