His approach actually is not that bad. Big two things:
1. His hips are collapsing at plant
2. When his plant (Left leg) comes down his throwing hand is already to his head
These are probably the two most common javelin problems amongst beginners to sub-elites….
1. Do some Multi throw work with Medicine ball (IE – hold ball overhead, run 5 steps, plant and throw – emphasizing keeping hands back till you plant the left).
2. Some HJ type take-off drills – focusing on the penultimate and the take-off.