How did you get the belt off in the first place? Here are 2 diagrams, one should be the correct path you need.
This one there is an adjustment bolt between the block and power steering tank (13 or 15mm). You also need to loosen the bolt holding the idler pulley below the PS pump (15mm).
This diagram should use the 3 bolts holding the PS pump, my old 88 XJ had this setup and those 3 bolts were a #$$# to get loose and adjust the tension on the belt.