All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad
is His slave and Messenger.
What is Islamically required of you is to advise the owner of this currency exchange company to fear Allah the Almighty and to refrain from invalid currency exchange transactions in which the receipt of one of the two counter-values is delayed beyond the contract session. As for you, given what you have described, you are not engaged in ribā, and no sin attaches to you for handing this man's money over to him, whether counted or uncounted, since this does not appear to constitute forbidden assistance to him in the ribā-based transaction.
Allah knows best.