Further to Bill's explanation, from my email to you (did you not receive?):
"In an Analysis panel, right-click the check box at left of a line. Or, in the horse header, with a paceline selected, click the ITM Contender box to make the horse Secondary or remove check from both Win and ITM boxes to make Non-Contender. Or – use the Contender boxes on the Entries screen to do the same thing."
Good luck Patrick!
Ted