First your need to enter your self employment income. This allows TurboTax to calculate the maximum amount you're allowed to contribute to your SEP IRA.
I followed the instructions provided for TurboTax Desktop. (Additional note: to search, click on SEARCH word in upper right of screen.) The TurboTax Help window popped up. I typed "sep-ira contribution" as instructed. The link "Enter my SEP IRA Contributions" lead me right back to this same page with the instructions.
So, the on-line help points me to a dialog box which points me back to the on-line help.
Unfortunately, the help is not providing me with an alternate (non-circular) path for navigating TurboTax to locate this entry field.
Here's how to Navigate to SEP-IRA Contribution:
Click on the Federal Taxes tab.
Click on the Wages & Income sub-tab.
Under "Retirement Plans and Social Security", click on Start or Update for "Business Deductions and Credits"
Click on Start or Update button for "Self-employed retirement plans" and follow the prompts