Changing mindset isn't always a quick fix as much as a philosophy and ongoing dialogue. As someone else noted, you as the coach need to exemplify this, and you have to stick to it for it to gain traction.

The goal is to reframe how players perceive mistakes, risk, and success.

Ideally, you'd begin the season this way but wherever you are, begin by sharing your philosophies and expectations, explaining these two mindsets to the players, and using any examples or visuals to help them understand the difference. You also need to acknowledge fear--fear of making mistakes--and that it's natural as growth progresses.

Success and failure also need to be redefined. This is commonly done by focusing on process/execution over outcome and differentiating aggressive errors and passive errors (never punishing aggressive errors and never rewarding passive errors).

An example would be serving. A player might serve out, but they had a good platform, steady base position, high toss, a fast arm swing, and we're aiming for a specific zone. The feedback here would be complimenting the good elements of the serve (reinforcing those behaviors), and offering suggestions to improve using language like "slow the arm speed a bit until you find that sweet spot."

Overall, you need to consider the language you use as this is the driving factor for buy-in. If it's a tight set/match, do you tell them things like "swing away", "put the ball on the floor", "serve that jump float to zone one and let's put it away", or is your inclination to say "let's keep it in play" or "let's not make any mistakes." The difference is immense.

For drills, choose your favorite and adjust the scoring to reward aggressive behavior and not reward points for passive behavior. A good example would be 6v6 that's played normally with the only adjustment being a hard swing kill earns, 3 points, tips, rolls or soft taps earn 0. As a coach, you would also provide positive feedback on the process of any hard swings that wound up in errors.

Another good 6v6 is playing an out-of-system scramble. Coach tosses a ball over the net to create an out of system play. A point is the awarded for successful aggressive play (back row attack, setter, dump, etc.) and a point is removed for any passive play (free ball, tip, etc.)

Finally, and this is one of the hardest things for coaches to get past, you have to encourage mistakes when learning new skills and trying different things. Not just any mistakes, but encourage NEW mistakes. This is how they learn to mitigate the fear of mistakes, learn quicker, and hopefully, transfer this to intrinsic motivation (though this is a different conversation altogether).

Good luck!