How do you correct a hanging columella? How is this performed?

Conceptually said the so-called hanging columella does not exist, it is a myth (except in elder patients); a columella may be exposed, be too visible and the caudal septum mucosa be exposed due to a series of factores, suitable to different corrections:
-seems you have alar rim retraction, could be a postop sequel of your rhinoplasty or maybe the rhinoplasty did aggravate a pre-existant issue; this needs alar batten grafting as caudal extension vectors to push down the alar rims to a neutral position-you show tip and columellar bulk, could you have any inside grafting? massive fibrosis? or is this just the shape of your infratip lobule? anyhow has to be adressedReturning to the topic, from a conceptual point of view the columella never hangs, when I say never is absolutely never except elder patients (very very old people), this is a deep misunderstanding based on the visual effect caused by your retracted alar rims due to poor lateral cruras or, associated sometimes, an oversized infratip lobule and thick medial cruras. In other words, the wings are short vertically and therefore disproportinate small, making a first glance impression that the columella is oversized (aka "hanging"), when the main issue is the short alae which are unable to cover the septal mucosa and match the septal leght.
Do not forget the location of the columella in a vertical sense is determined by the caudal septum, conceptually the septum does not "hang", to the contrary, it is neatly clear from your pic that the nostril "sil", the base of the nostril, is horizontal as it sould be.
The treatment for congenital or acquired alar retraction is the lateral crura grafting, even composite grafting (I don't opt for the composite grafting, I prefer pure cartilage grafting and adding the lining without a graft but with the undermining of a mucosal flap).A, correctly said, prominent columella show can be of TWO kinds, which are really three:
-PROTRUDING columella: the columella is so prominent (due to thick or broad medial cruras and thick subseptum, or due to ethnicity like in arab noses with too long lateral cruras pushing down the medial cruras and making the infratip lobule prominent) to arise in excess (normal is 3-5 mm) below the nostrils or alae level
-EXPOSED columella: the columella is not prominent or oversized, it is just the alae or nostrils suffer alar rim retraction, congenital or iatrogenic (after rhinoplasty) and do not cover sufficiently the columella
-hybrid situations, not uncommon, in which part of the problem is a protruding columella and other part can be attributed to rim retraction; this is a tricky situation and can be misdiagnosed by the surgeon, tending to think in black and white terms putting all the blame on the columella or the alae, which can be catastrophic or in the best case end in merely partial correction
Once again, excepting very old patients, columella is not a hanging part.
The treatment protocol is as follows:
-protruding columella: address the cause, normally this is best done with powerly thus very delicate tongue-in-groove securing technique by which the medial cruras as narrowed and lifted up using the pre-existant or newly built caudal septum
-exposed columella: lateral crura customly designed caudal extension batten grafts (some surgeons advocate the composite grafts, as said before I don't like them, unreliable)
-and in hybrid scenarios might be the former both together
Correcting an exposed and or protruding columella is not a simple maneuver and should be done ONLY by highly experienced surgeons, you run the risk of ending with a sunken columella piggy-style or something worse. It is a top-notch surgical maneuver.

The hanging columella is composed of excess cartilage and skin, which are both trimmed back on the inside of the nostrils. This can be performed under local or general anesthesia, depending upon the patient's preference. For more information  and many before-and-after examples, please see the link and the video below