When a conifer starts dying like this, there's no way back, sadly. Unlike "normal" trees and shrubs, pines grow from the tips - once they die, they stop growing. They don't re-shoot from lower down on the branches or trunk. Sadly there's nothing you can do. It is possibly diseased, so remove it as soon as possible. Replace the soil in the planting site and get another in next autumn - don't plant in summer as it stresses the plant too much.
Conifers are susceptible to a range of incurable viral and fungal diseases including cankers. These can be quite devastating so prompt action is needed.