How can the stolen funds be returned to the colleagues without anyone knowing, and is it possible to help with that?

Theft is a grave sin that necessitates repentance. The conditions for repentance are: abstaining from the sin, regretting having committed it, and resolving not to return to it. If the sin involves a human right, a fourth condition is added: fulfilling the human right by restoring it or seeking forgiveness from the person after informing them, based on the Prophet’s (peace be upon him) saying: "Whoever has wronged his brother concerning his honor or anything else, let him seek his forgiveness today before there will be no dinar or dirham, and if he has good deeds, they will be taken from him to the extent of his wrong, and if he has no good deeds, then some of the bad deeds of his brother will be taken and put on him." If direct return of the money is feared to cause scandal, the money can be delivered to its owner through indirect means, such as an anonymous message or by giving the money as a gift.