When on the "Create" a campaign section (i.e Contest, Giveaway, Refer A Friend, etc.) there is absolutely no way to get back to the previous page other than hitting "back" on the browser.
For usability the top PZ navigation bar should always be visible for easy navigation no matter where on the site you are.
Edit: There is a "Go back/Continue" set up buttons when building the campaign but this might be better served to be some sort of breadcrumb navigation to highlight what step you're on and easily jump around in the steps for the campaign once you've been through a step.
Something like "Templates" per my sample above could be used to navigate to your different PZ walkthroughs similar to this. 👇
Just so long as that navigation is always accessible.