What is the ruling on purchasing a computer and clothes with illicitly gained money from impermissible advertisements? Is it permissible to donate the equivalent value of the illicit money as charity while keeping the computer? Can this charity be paid in installments?

You have done well in abandoning the forbidden work. The completion of repentance is to dispose of the money earned from it by giving it to the poor and needy.

The things you bought with this money (device, clothes) are permissible for you to benefit from; you are not required to sell them, and their sale price is lawful.

What is required of you now is to give out the amount of the unlawful money (600) either in one lump sum or in installments, if you spent it while you were not in need of it. However, if you were poor and needy when you spent it, then nothing is required of you, even if you become well-off later.

If a poor person spends from unlawful money due to their need, it does not become a debt upon them. But if they spend it without need, or if they had lawful money that sufficed them, then they are transgressing, and they must clear their conscience upon repentance.