Or through exhalation and retention of the breath.

Patañjali introduces here prāṇāyāma as a method to stabilize the mind. Pracchardana is controlled exhalation; vidhāraṇa is retention.

Long, controlled exhalation activates the parasympathetic nervous system, inducing calm. Retention stabilizes vital energy and quiets thoughts.

This sutra anticipates the more detailed explanation of prāṇāyāma in the second pada (2.49-53). Here it is mentioned as one of many available techniques. The connection between breath and mind is direct: by controlling one, you influence the other.