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