How to update custom content type fields value in bulk?
Without a lot of detail about your problem I suggest you research these modules: 


Views Bulk Operations (VBO)
Views Bulk Edit
Feeds
documentation for the Feeds module for Drupal 8


VBO works through Views: you create a list of the nodes you want to edit. VBO provides a field through which you can select nodes (checkbox) and then you can perform operations on them. 

Feeds can update existing nodes from a CSV file (create new nodes too). They're a bit trickier to configure, mapping must be tested thoroughly and you need to make sure the entries are unique, but once you have them set up correctly you can use them over and over again.