Beak Trimming should only be completed by an Avian Professional, like a CAV or a CAVT. The nerve mass at the base of the upper Beak is highly sensitive. Over trimming is common when the work is done by the uneducated. This commonly results in the Parrot not being comfortable eating. And, that can turn into a serious problem quickly.
That all said, as part of understanding plucking, it has been found that removing the point of the upper Beak can reduce irritation of the skin and in 'some' Parrots, reduce plucking.
Over-growth is more commonly an issue of diet /illness. Then followed by limited use of the Beak. Your first (very soon, after bring the Parrot home) Well Parrot Avian Vet Exam should include that discussion. If your Parrot's Beak is overgrown, the recommended full blood screen should provide indications as to what direction you need to proceed.