II.54 Withdrawing the senses, mind and consciousness from contact with external objects, and then drawing them inwards towards the seer, is pratyahara. – Iyengar.
While this is sometimes translated as “restraining” the senses, it is more a channeling, or turning inward of the senses. Truthfully, “restraining” the senses and the mind’s response to sensory input is like telling a river to stop running.
But you can build up the banks and teach it a new path. So through the focus of asana and pranayama, and the self-study and surrender, the sense organs, or organs of perception, turn in on themselves (sva: own, their own) not focusing on external objects.
The mind is given something with which to busy itself.
II.54 svavisaya asamprayoge cittasya svarupanukarah iva indriyanam pratyahara