What are the water parameters?
Tank size?
Filtration?
Maintenance schedule?
Foods?
Tank mates?
When was the last fish introduced? Was it quarantined?
How long have you kept the fish?
What other symptoms have you observed?
Color of poop?
Normally, when a fish scratches especially on a frequent basis, there are plenty of things that can cause it.
1. Silt irritation
2. Flulkes
3. External parasites (fish lice, ergasilus, fish leech, anchorworms)
Until you are sure of the exact cause of this issue, do not attempt to treat.