where do I enter self employed retirement plan contribution (salary deferral)? TurboTax says look for "other business situations" , but I don't see that!

Using TurboTax Home and Business desktop version:  

• Go to the Business tab at the top of the screen, click Continue and then I'll choose what I work on
• Scroll down to Less Common Business Situations
• Click Start or Update beside Self-employed Retirement to get started

If you are using TurboTax Online, go to Wages and Income on the left side of the screen.  Then scroll toward the bottom of the page to find Other Business Situations.  It should be almost at the end of the list, just above the blue Done with Income button.