How to change altitude of flight

[Edwin]

Hi, i'm using local_planner and ive set my takeoff height and my goal_z param to 2m. During its flight to the goal_z, the drone will tend to fly till a height of 6m before it decent to the way point. This happens with and without obstacle. May i know how to i change or edit so that it will not constantly fly till 6m height. Will appreciate the help! thank you!