Separate classes with separate entries that are held at the same time with all the entries from all the classes either in the arena together or running back to back to the same judge(s) are said to be concurrent. HSW allows classes with separate entry fees and results to be connected in a such a way as to have one draw and for entering results without having to know which entries are in which class.
When in the Go area of a class being added to a show, the Held With field tells HSW which classes to run concurrently. By default, the Held With will be the class code of the class you are adding to the show (all classes are held with themselves). All classes running concurrently will have the same Held With class code.
For AQHA Leveling, change the Held With of the Level 2 class to the class code of the Level 3 class (which should already be listed in your showbill).