What should a person working abroad do, who has a bank account in Egypt, and forgot to close the interest-bearing account, and now wishes to dispose of the interest money that has accumulated over three years?

You must repent to Allah and close your account in the usurious bank, and open an account in an Islamic bank that operates according to Sharia principles. As for the previous usurious gains, you must dispose of them by spending them on the welfare of Muslims and in charitable endeavors. It is not permissible to benefit from them. If you do not know their amount, request it from the specialists at the bank. If that is not possible, strive to ascertain what you predominantly believe covers the usurious gains.