If the wheel was straight before, then the most likely thing to have changed it is one of the front tires has taken some sort of a hit. Set the steering wheel straight and sight up the front tires. If one is not straight, that is your victim, adjust the tie rod until it matches the other. If both are not straight, and you cannot move the steering wheel, adjust both until they are straight. Having someone hold the steering wheel straight may be necessary. Most vehicles have the wheels toed in slightly, meaning if the front wheels are both straight, the front of the wheels are slightly closer together than the back of the wheels. If you find anything bent during this process, you will likely need to replace it. Then take it for a drive. If you have it right, you will likely be able to tell.