There is a new Option Reindex List and Reindex document library that allows users to force the Content of list and library to be re-indexed. So it means the whole list or library to be picked up by a Continuous crawl, regardless of whether the items have actually changed.
Go to document library settings – Advanced Settings
Click on the below Reindex Document Library or Reindex List
It will prompt the following
Now the whole list or library will be picked up by a Continuous crawl