I don't think you can use TurboTax to prepare only one individual form, especially considering the fact that you didn't use TT to prepare your 2017 return.
I'll link you to the instructions for 2018 form 8962, which may assist you in preparing your 2017 form.
https://www.irs.gov/pub/irs-pdf/i8962.pdf
If you are unable to complete the form using the instructions, I'd recommend consulting a tax professional for assistance.
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*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
