In pairs half a metre from the net players volley the ball cooperatively over the net moving side-ways until they reach the end of the net.
Players then move back to the 3 metre line and volley the ball high to each other moving the opposite way until they reach the other end of the net where they move back close to the net and repeat.
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.