How can a repentant person return stolen goods or their estimated value to the company without revealing his identity, knowing that some of the stolen goods have been completely consumed or damaged?

Your friend has done well by regretting his actions, and his repentance requires him to return what he took, for the Prophet, peace and blessings be upon him, said: "On the hand is what it took until it returns it." The stolen item must be returned if it is still in existence, or its value guaranteed if it was consumed, at its worth on the day it was taken. If anything remains, he should return it as it is. What was consumed should be valued on the day it was taken, and he should deliver it to the company, even through indirect means. If he does that, seeks forgiveness, and resolves not to return to such an act, then he has repented completely.