16 years old girl has burned her leg at level of knee joint she has been recovered in 2weeks what do you sugesst to treat the scar region?

1st degree burn? If the burn is 1 st degree and closed you can use bio oil over the counter. Try it on one area first, if the skin is not adequately healed wait before using. It will decrease the tendency to raised s ar tissue. A pressure dressing can also be used such as an ace or elastic bandage at about 5-6 weeks after the injury if it shows signs of developing raised scar tissue.
Multiple. The most important treatment is a burn scar compression garment with silicone gel built into the garment at the area of the scar. Continuous use of this garment for three to six months will significantly improve scarring from burns and from skin grafts. Aggressive massage with a non-comedogenic (doesn't clog pores) moisturizer is critical, too.
Compression. Compression dressing and silicone sheeting is what i suggest as a preventative step. Other treatments are a possibility but have some down sides. Discuss with your plastic surgeon.
1st & foremost-- ...Keep the sun off it: it will always be prone to hyper pigmentation. To prevent thickening, compression garments, silicone gel sheeting, paper tape, mederma are all helpful. Multiple factors determine best approach. Tretinoin may have a role.
Knee burn. Supervised treatment under the guidance of a physician and physical therapist experienced in wound care and the topical silicone gel sheeting, pressure dressings, range of motion exercise/massage, avoidance of sun exposure and close observation.
Massage, stretch. Scar massage is very, very important when burn scars are near joints. Many people use cocoa butter for this but there are products like mederma which also work, but are more expensive. Vigorous massage twice a day (slightly uncomfortable, at first) is best. For severe scars, silicone gel sheeting or compression garments may be needed. She should also straighten her knee all the way 3-4 times a day.