If you are experiencing a crow on the high A but have no sandpaper to hand, try using your thumbnail. Slowly drag your thumbnail across the tip of the reed at an angle. It must be done quite gently to avoid chipping the edges.
Ensure that you do this in one direction only and to both blades. This will scuff up the edge and produce the same result as using sandpaper. Check in the pipes after each pass.
Squealing plastic practice reed
Just because your practice reed is plastic doesn’t mean it doesn’t require adjustment. If your plastic practice reed is squealing, you’ll need to sand the blades a wee bit.
Using very fine sandpaper, 320 grit or below, sand the top half of the reed very carefully on both sides. This should remove the squeal. Repeat as necessary.