Previous button got problem

my previous button got problem.

Look at my attachment.

The ‘1’ ,‘2’ and ‘3’ buttons is show step 1,step 2 and step 3.

The ‘next’ button will track the step that already show and show the next step that haven’t show. That mean if u click ‘1’ button and ‘2’ button.Then u click ‘next’ button, the step 3 will be show.

My previous button cannot work as what i want in next week.