The ability to run DO through your PreApp account is dependent on your Integration settings.
Click the Gear Icon on your dashboard, select System Settings and click PreApp Integrations on the Nav Menu to the left.
Use the gears to the far right of the Fannie Mae option to open the FannieMae Settings Page.
Fill out the first and second sections.
Open a file and click DU/DO on the Nav Menu to the left.
Click the blue Start DO button.
Make a selection for both drop downs, then click the blue Submit DO Request button to generate findings.