It's all relative.

The sharping lever simply moves a pin against the string to shorten the string and raise the pitch - i.e. to make the note the string sounds sharp relative to the pitch when the lever is not engaged.

If you tune it with the sharping lever pin against the string, when you move the lever the other direction, the pin is removed, the string is longer, and the note goes flat.

The pin simply acts like a fret. On a guitar you move the string aginst the fret by pressing on the string. On a harp you move the fret against the string by turning the lever.

If the change in pitch is too large, the pin is too far from the open end of the string, and needs to be moved up, closer to the open end of the string.

If the levers are like the ones pictured in the pdf, you should be able to loosen the screws slightly and slide the whole lever mechanism up slightly, and retighten the screws. If you can't move the mechanism far enough, it may be necessary to make new holes for the screws.

It's possible that the mechanism was properly located but has slipped, in which case just moving it back to the correct location and tightening the screws carefully is all that's needed.

John