Think about the amount of time that you spend at work. Thousands of hours per year, right? That's a lot of time to spend with someone if you happen to dislike him or her. In most cases, people get along fine with others at work.
Years ago, Chris Rock included in his stand-up act a bit about when people feel they have enemies at work. Comedians naturally gravitate toward discussing such topics because everyone can relate. Often you get along with most people at work, but one or two people can drive you crazy.
Having this experience at work is a great opportunity to learn how to become more flexible and to mentally do some work to accept someone who you might not otherwise like. The truth is that we can choose our friends. Like our family, however, we can't choose our co-workers.
If you have a co-worker who you don't like or who you can't stand, work hard to see them in a different light. You have your reasons for not liking them. It is not worth wasting mental energy disliking someone whom you have to see almost every day of the year. Accordingly, try to come up with a list of characteristics they have that are positive. If you can't think of any, think of how this person might be important in someone else's life. Maybe that person is a good aunt or uncle to a niece or nephew somewhere. Also try to think about their past. What experiences did they have that could have changed them and made them difficult or unlikeable to you.
I believe deep down people are good, and that we all would be more likable if we knew how to change the parts of us that even we don't like sometimes. Learning to have sympathy for someone, not pity, is a great way to see someone as an ally.