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 obligatory upon you is to repent to Allah Almighty for the deception and dishonesty you committed. This includes seeking forgiveness, feeling remorse, and firmly resolving not to return to such behavior.
As for the salaries you received - whether it is permissible for you to benefit from them or whether you must return them, either fully or partially – that ruling depends on the reality of your work in the company: Did you perform your duties as required? How much did that person’s assistance affect your performance? Did your employers know what you had done and still agree to pay you, or were they unaware of that?
All of these factors influence the ruling, and we cannot assume scenarios and issue rulings based on possibilities that may not even exist, as that would further complicate the matter.
Therefore, our advice to you is to consult a knowledgeable scholar in person and present your case to him.
Allah knows best.