Move the copter to a new waypoint

Suppose that the copter is implementing a mission, let say on waypoint 20, and now I want to go back to waypoint 2 or any other waypoint directly. How can I do that?
Many thanks in advance.

if you are using GCS mission planner you can set the heading waypoint to 2 and press go to button directly.

Thank you. However, I was talking about the Mavlink method