You will be able to perform a bulk operation to reactivate the subscriptions on your Chargebee site. You will need to navigate to Settings > Import & Export Data > Choose a Bulk Operation in your Chargebee site and make use of the 'Reactivate Subscriptions' bulk operation to reactivate the subscription.
If you are to perform a bulk operation for existing data from Chargebee you may have to export the data from Chargebee and update those data to the import sheet from Bulk Operations. Earlier the export data format and import data format varied which involves a lot of manual intervention. With the new enhanced Export file option, you can either export a file using Download Data or use Download import-friendly file from Settings > Import & Export Data > Product Catalog. Refer to this link for more information.
It is highly recommended that you try this on your Chargebee test site before performing the 'Reactivate Subscription' bulk operation on your Chargebee live site. Do click on the link mentioned below to view the documentation for bulk operations on Chargebee.