3 blockers and 3 players on a bench;
Players on the bench take it in turns to throw the ball (quickly) to each other. On the third catch the player slaps the ball and hits at net height, through the block;
Blockers track the ball and move to block accordingly.
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.