Bobbie:

Lay the harp on its back and remove the two plates which secure the ends of the bars. Don't pick the harp up or the bars and springs will fall out. You can now see what the ends of the bars are doing when you push them down. If you want to keep them from moving so much, you can shim the ends of the bars either on the sides or on the end to prevent motion in those two planes. Don't shim them too much or they won't move smoothly.

Or, as Bill D says, you can just be careful to press them straight down.

Bev and Jerry