To move toward the second jhāna, you want to do a foreground-background reversal. When you take the deep breath and deeply exhale, both the pīti and the sukha calm down in intensity, but the pīti drops much more in intensity and is now low-grade and more in the background. The sukha, although perhaps now a bit less intense than it was before the deep breath, is still strong enough to now be the more prominent of the two. The “inner tranquility” mentioned in the description of the second jhāna reflects the shift from an experience of pīti and sukha to an experience of sukha and pīti.
