Thanks for writing. Unfortunately with reblooming iris, there's no guarantee of the rebloom --- it depends on a lot of factors, including spring, summer, and fall weather conditions, as well as the variety (some, like 'Immortality' are more reliable than others).
Be sure your iris are in full sun with well-drained soil. Don't water or feed them much during the summer as they take a rest. Also: How old are they? If the clumps are large and you've not divided them, they may be getting too crowded to reboom.
---Justin, Senior Garden Editor, BHG.com