What is the ruling on working in computer maintenance and entering phone numbers for a company that sells halal products, but one of the companies it deals with offers alcoholic beverages as gifts to those who buy its products, and is it permissible to leave the part related to this company to a colleague?

If your company gives alcohol to its customers when selling its products, this is forbidden due to the generality of the Hadith: "Allāh has cursed alcohol, its drinker, its server, its carrier, and the one to whom it is carried." Agency in sin is forbidden. As for your work in maintaining computers and similar tasks that are unrelated to alcohol, it is permissible. You should advise your company to stop dealing with those who give alcohol as gifts.