This video shows how to replace key hammers in Casio keyboard . If some of the keys are lower spaced compare to the other , you can fix it by watching this video
AU$1.57 | Casio Replacement Hammer Rubber Caps For AP 200 245 260 270 450 460 AP6BP CDP 130 135 220 230 CGP700 PX 130 135 310 320 PX3BK
https://a.aliexpress.com/_mOeltgU