I have done a private investment and that company went bankrupt. I need to file form 8949. How do I do that using Turbo Tax Premium Online version.

Here is where you will enter the information. 

1.  Go to Wages and income
2. Investments and Savings (1099-B, 1099-INT, 1099-DIV, 1099-K, Crypto)
3. Add investment
4. When it asks for the type of investment, select other
5. When you arrive at the sale page and it asks for the type of investment, indicate other.
6. Continue through the sale page listing proceeds, dates etc. and finish the section. The information you place here will then create form 8949.