1999 arctic cat panetera 800 reverse gear not engaging it smake a grinding noise how do i fix this.?

you probably need a new reverse gear. Take off the chaincase cover and inspect your gears for wear. You should be able to tell if they are worn, even w/o alot of mechanical knowledge. Hopefully it's just an adjustment needed. If you need the gear(s), I can probably help you out 315-964-2577