WARNING: This page is about a different car, the 2014 Mitsubishi Outlander. However, it is still accessible from the selected car via links, so may be relevant.
Use special tools MB990767 and MD998719 to prevent the camshaft sprocket from turning, and then loosen the camshaft sprocket bolt.
Fig 1: Rotating Camshaft Sprocket Bolt While Holding Camshaft From Turning