Since I incorrectly assign the page onto the wrong template, I cannot undo the changes by drag-and-drop page from the wrong template back to the unassigned page list. Is it normal?
In the second scenario, I try to reassign the page with different template. But I am unable to drag-and-drop the page to a different template which is shown on a different pane. I also cannot find any CM1 button to move the page to another template. Is it normal?
Please see attached screenshot for details.
Your first scenario is normal - you cannot drag pages back to the Unassigned menu. One thing you can do is create a new template based off of one of these pages you don’t have a template for yet, name it your “Unassigned” template, and use this as a temporary home for all of the pages that don’t have a template yet.
The second scenario is a known bug. The current workaround is to temporarily rename the destination template so that it sorts alphabetically next to the source template, or edit the page and use the original Actions > Change Template functionality.