Is It Permissible to Train Others to Deal With Banks?
Question

I work for a company that deals with the banks and I used to be the company’s representative with the banks, but praise be to Allah, I have repented from that job. But I handed over my work with the banks to someone else who would deal with the bank instead of me. If what I did is prohibited, what do I have to do? Now he is working on the basis of what I taught him about how to deal with the banks.
Praise be to Allah.If one’s dealings with riba-based banks is limited to depositing money in current accounts without any interest because there are no Islamic banks and because companies need to do that in order to protect the money and make it available for trade, there is nothing wrong with it. 
But if the dealings with them involve prohibited issue such as borrowing from them directly or in other ways such as buying through them or opening a line of credit with them etc., then these dealings are prohibited and it is not permissible for anyone to engage in them, because that is cooperating in sin and transgression, being a witness to Riba (contracts), and approving of it.  
Allah says (interpretation of the meaning): 
“Help you one another in virtue, righteousness and piety; but do not help one another in sin and transgression. And fear Allah. Verily, Allah is Severe in punishment.” [Al-Ma’idah 5:2]
Additionally, Muslim (1598) narrated that Jabir (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) cursed the one who consumes Riba, the one who pays it, the one who writes it down and the two who witness it, and he said: “They are all the equal (in sin).” 
Based on this, since the company's dealings with the banks is in this manner, then you did well to leave this job , and we ask Allah to accept your repentance. Nonetheless, you were wrong to teach it to someone else , because that is teaching and helping him to do something prohibited. In that case, you should have explained the Shar`i ruling to this brother and advised him, as well as repenting to Allah. If he responded, then praise be to Allah, and if he did not, then you have still done what is required of you. 
We ask Allah to guide you. 
And Allah knows best.