If you select the Complete Enumeration experimental design method (on the Design tab) rather than Balanced Overlap, this will happen.
This will lead to minimal overlap for all attributes, not just the first attribute. Meaning, the design algorithm will not repeat a level within the same task unless forced to do so (e.g., there are fewer than 4 levels in the attribute, but you are showing 4 concepts per task).
Some level overlap on the other attributes may be desirable in some cases. If so, there are power tricks that could be done to massage the design such that the first attribute had minimal overlap and other attributes had some level overlap.