What is the ruling regarding my working at KFC restaurants for three years, based on previous information about its permissibility, given my later discovery that its meat is not ritually slaughtered? Is it permissible for me to eat its fried meat, and what is the ruling regarding fish fillet sandwiches?

For poultry and meat sold in Muslim countries and elsewhere to be permissible for consumption, it must be slaughtered according to Islamic law, and the slaughterer must be a Muslim or a person of the Book. If these restaurants do not slaughter the chickens according to Islamic law, it is not permissible to eat from them or to work with their owners. It is permissible to eat fried meat and fish from these restaurants, provided that they are not fried in oil or utensils used for unslaughtered chicken, and that the meat itself is halal (definition).