What is the expiation for an employee taking for himself gifts intended for customers, given that he is unable to confess to the employer?

Assaulting people's wealth is forbidden. Whoever is entrusted with distributing money must be trustworthy and give completely what they have been commanded to give. The money you took, if it belongs to clients, must be returned to them or you must seek their absolution. If it belongs to the employer, it must also be returned to him. If you cannot directly inform them, then send it to them secretly and repent to Allah with sincere repentance, and increase in good deeds.