What should a person do who regrets earning money from a previous job through unlawful means, does not know the amount, and how should they act when returning the money to the company or donating it as charity?

Your feeling of remorse is the first condition for repentance, followed by abandoning the sin and resolving not to return to it. The fourth condition is to return what was wrongfully taken to its rightful owners, by returning everything you took from the company. If you do not know its exact amount, you must pay what you deem sufficient to settle it. You can inform the responsible party at the company and ask for discretion, or you can pay the amount by undertaking tasks that require funding and refusing to accept payment from the company, while ensuring that the right is delivered to its rightful owners and maintaining your confidentiality. Allah Almighty says: "And whoever fears Allah - He will make for him a way out And will provide for him from where he does not expect."