What is the ruling of Islamic law on continuing to pay installments for a laptop purchased with a credit card after learning of its impermissibility, and is it obligatory to sell the device to pay off the installments, or should one complete their payment from their salary?

There is no harm in paying for purchases with a credit card from one's salary. There is no obligation to sell the device you bought with it, because the prohibition related to dealing with this card pertains to the person's liability, not to the money itself or what was purchased with it.