Set the track bar so that the front wheels are centered under the Jeep ie the same distance from the outside of the frame rail to the inside of the brake disc. There is no side to side adjustment on an XJ after you have the front axel centered take it to for a 4 wheel alignment.
Are you talking about the front or rear? For the front unbolt the track bar and jounce the front end untill the jeep looks centered, then adjust the track bar to fit. The rear has no adjustment, if it's off then something is installed wrong or broken.