What should an accountant do regarding the manipulation of company profits to reduce the CEO's share, and should he inform the CEO about this?

What your company manager asks of you, regarding lying, falsehood, and injustice towards the executive manager, is forbidden. So, do not respond to his request, and advise your manager that what he is asking for is impermissible. If he insists, then inform the executive manager, if you are safe from harm. Do not do what he commands you to do, as Allah Almighty says: "And cooperate not in sin and aggression. And fear Allah; indeed, Allah is severe in penalty." (Al-Ma'idah: 2).