The spindle is misaligned by a degree or two
Oh dear! that's a serious problem. (Are you sure the spindle is that far out?)
The head is held in place by four bolts in the corners, but is dove-tailed to the bed. There is a clamping screw in the rear to pull the head over to the front of the bed (like the tail-stock).
You could try loosening the four bolt and tweeking the clamp bolt in the hope it'll square up a little, but if it's really move that much it might have damaged the head or the bed or both.
If you want it fixed properly go to someone like Paul Babin - you better be sitting down when they quote the price !