Is it a condition that the questioner ask the other partner for forgiveness face-to-face or return his money, after one of the partners forgave him and promised to inform the other?

It would have been better for you to ask for his forgiveness yourself, but since you appointed his other partner, the agency is valid according to the majority of scholars. You owe nothing to either of the partners, and you must repent and seek forgiveness for what you have done.