The most common way that I see golfers hit the middle of the ball(blading) is because they try and swing up on it to much, or try and lift the ball off of the ground.
Their tendency is to hang back on their trail leg and lift. Ironically this can also lead to hitting behind the ball as well.
They need to realize that when the ball is on the ground they need to strike the ball and then the turf. You don’t need to take a massive divot, but you need to move a little turf after striking the ball.
A good drill for this is called the Flamingo drill. Narrow the stance, putting most of the weight on the lead leg. Drop the trail leg behind them(away from the target line). Make some L-swings keeping the weight on the lead leg the entire time, the trail leg will just be for balance.
This should give the golfer a nice feeling of swinging down and through the ball.
Make some practice swings to start, seeing the club striking the turf on the target side of the ball. Once comfortable with that then try to do the same swing with the ball. Do not over swing, the goal is to try and get a feeling of swinging down and through the ball.
It’s just a drill, it is not meant to play golf this way, but isolating the feeling can help once they go back to a full swing.