It is very easy to change the position of the “Plan Chapter”.
Simply you just need to drag & drop chapter to change it's position.

See the below screenshots.

Step 1: 

Navigate to plan builder and see the left sidebar.

Click onto the “Dots” appearing on the plan chapter.

Step 2: 

Hold the “Dots” and drag it to the position, where you would like the “Plan Chapter” to appear. 

This will change the position of the particular “Plan Chapter”.