How can I repent from buying the forbidden (Hotbird) lens, knowing that I cannot destroy it because I share its ownership with three other people?

You must initiate sincere repentance, which involves completely abandoning and getting rid of the tool that brings corruption. If you are unable to do so, then you must distance yourself from it and from bad companions until they repent, for Allah says: "So fear Allah as much as you are able." You should associate with the righteous and good people, and know that Allah is aware of your secrets and your open deeds, and He accepts the repentance of sincere penitents, for Allah says: "Indeed, Allah loves those who constantly repent and loves those who purify themselves," and His saying: "Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.""