You can login to the admin module and do a search on incompletes.
Select Search from the menu, select "Incompletes" as the Respondent Status and then click the "Search" button.
A list of IDs will appear. You can select any of these IDs in the list and click on the DELETE SELECTED RECORDS option.
Now you need to be careful here because you may have a respondent or more actually completing the survey as you go to perform this process. At the time, they will be classified as Incomplete. So best you do this exercise at a quite time like late at night or very early morning.
You can also download your data to a CSV file and go into Excel and carefully select incompletes and remove them. Then load the edited file into Sawtooth Software.