Stand facing a partner on the other side of the net and about 1 metre behind the 3 metre line; throw the ball using two hands underarm over the net to land on the 3 metre line. Keep repeating until accurate.
New hitters rarely miss because of their arm. They miss because of their feet. Build a reliable approach, then time it with your setter.
When your hitter gets stuffed, five teammates standing and watching is how you lose the point. Good attack coverage turns a blocked ball into a second swing.
Coaches spend hours correcting arms in serve receive when the real fault is almost always the feet. Fix the movement and the platform fixes itself.