Yoga Sutras 3.48
Patanjali, explained by Swami Vivekananda
ग्रहण-स्वरूपास्मितान्वयार्थवत्त्वसंयमादिन्द्रियजयः ॥
grahaṇa-svarūpāsmitānvayārthavattvasaṃyamādindriyajayaḥ
By making Samyama on the objectivity and power of illumination of the organs, on egoism, the inherence of the Gunas in them and on their contributing to the experience of the soul, comes the conquest of the organs.
In plain words: By focusing deeply on the senses, on how they reach out and show us things, on the sense of 'I' involved, on their qualities, and on how they serve the soul, the yogi gains control of the senses.
Swami Vivekananda explains
In the perception of external objects the organs leave their place in the mind and go towards the object; this is followed by knowledge. Egoism also is present in the act. When the Yogi makes Samyama on these and the other two by gradation, he conquers the organs. Take up anything that you see or feel, a book for instance; first concentrate the mind on it, then on the knowledge that is in the form of a book, and then on the Ego that sees the book, and so on. By that practice all the organs will be conquered.