Scroll Versions does not officially support bulk version changing (although we do currently have an open request for this feature).
We actually do not recommend bulk changing the version of multiple pages, as in most scenarios, a combination of unversioned pages and fallback pages works perfectly well.
Let's quickly explore how versioning works and how why unversioned pages are fine in most cases:
Pages becomes versioned either when they are first edited in a version, or when converted to a versioned page using the Scroll Versions dropdown. For example, if a page has not been changed from version 1.0 to 3.0, but is then changed in 4.0, then versions 1.0, 2.0, and 3.0 will point to the same page (version 1.0) and version 4.0 will be created on a new page. There is no need to create additional pages for versions 2.0 and 3.0, as the content is the exact same as it is for version 1.0.
That is why Scroll Versions also uses the concept of a fallback (pages in later versions being the same as the page as an earlier version it has not been changed, for a full explanation see the term 'fallback' in the glossary), to not duplicate the content unless it is required. This is important in larger spaces, as creating new versions of hundreds of pages with the same content would be extremely inefficient.
How to execute a bulk change
However, if you still want to execute a bulk version change, you can do so by importing multiple existing Confluence pages to a target version.