I retired recently and have spent a lot of money trying to move to Tennessee. Things did not work out, I can't afford to move to Tennessee and now I want to sell the mobile home I bought 4 months ago.

I have been told I have to live in it for one year before I can sell it as a private person.

Is this true? Where can I find the exact law to read it?

No, you may merely sell it, you are not a business or in business of selling mobile homes. You may want to also ask this question from a tax view point but my guess you may end up losing money on the home anyway

I think you misunderstood 'have to live in it for one year.' You probably will just pay a higher tax.
Here's one guide, but you really need to talk to a tax person yourself, because of various definitions of mobile and manufactured homes that only you have information about, regarding yours.
https://www.tn.gov/revenue/taxguides/salesanduse.pdf