I transitioned from a sole proprietorship to a single owner S-Corp in 2016. What do I use for the initial shareholder basis for Form 7203?

My small business was a sole proprietorship from 2001 to 2016. In 2016 I transitioned to an LLC S-Corp. I am the single owner and 100% shareholder. My business showed a loss in 2021. I entered this from my K-1 and TurboTax is asking me to complete Form 7203. I do not  know my stock basis and am trying to calculate it from my previous years K-1 statements. However what do I use for my initial shareholder basis? As I did not purchase the company/shares in 2016, I just changed the status of my business.

 

Thank you very much for any guidance.