The Horned One in the Llewellyn is shown as a wild man of the woods, meditating alone, covered in animal pelts with only a wolf, lying down a little way away, for company. It's a different image, and symbol, from the traditional Tarot Devil.
From this image, and from the myth associated with it, I would say what this person needs is to reconnect with their instinctual nature, away (at least mentally) from the trappings of civilisation, and time spent alone to be free from any bonds that have forced them into a mold that doesn't belong to them. Sometimes it takes having to go to the depth of being - and despair - in order to reach that place of sanity and freedom. They also need to be in nature - I mean real nature, not a garden or a park - in the woods and mountains. A weekend or vacation far from the madding crowd in a totally natural environment, roughing it a bit (camping perhaps) will do them the world of good.
If you are asking what this person needs, I am assuming you think they need help. It seems from this card that the help they really need is to be left alone - with just some discreet unspoken presence (like the wolf in the card) to let them know they have company when they require it. Wolves are very nurturing, but not demanding. That wolf has also accepted to be away from the pack to keep the Horned One company.
