Multisite feature is available only using Berta.me Pro and Shop plan. 

You can swap all content between two sites. This feature is particularly useful when redesigning your site — you can create a new unpublished site and, when ready, swap its contents with your production site.
 
To swap site contents use the Multisite menu item from the main navigation. From the list of existing sites, click the swap icon next to the site you wish to swap.

In the dialog window, choose the site you want to swap contents with, then click the Swap button to proceed.