Beak trimming should not have to be done on most healthy birds. If your bird’s beak does overgrow, you may have a nutritional problem. Take the bird to a veterinarian.
Sometimes a bird’s beak is somewhat deformed and may cause overgrowth. Many baby birds beaks that are deformed can be corrected by an avian veterinarian with brackets. Many birds beaks cannot be corrected.
If you do buy a bird with a beak deformity, plan to make several trips to the vet a year for proper trimming. Unless you are very experienced with birds, I don’t suggest you try this procedure.