At the corner that is low, look at the leg leveller. If they have a hole through the center of the threaded rod in the foot, put a screwdriver through there and turn it. Should turn to the left to raise the table at that corner.
If there is no hole in the rod, you'll have to take just enough weight off that leg to turn the foot. If you're looking down on top of the foot, you should turn it clockwise to raise it.
If the ball is only rolling out 1/2" or so over the length of the table, you might only need to give it a quarter turn or so, so don't over do it. You won't want to lift that table any more than you have to, even just taking the weight off like that. Good luck!