How to manually clear Case Flags History Tracking records
Case Flags History Tracking records accumulate over time based on your Organization's Case volume and the number of interactions per Case.
With your Organization's data storage capacity in mind, you may choose to export Case Flags History Tracking data from Salesforce to perform data analysis, and manually delete records as needed to free up space.
Ensure you've enabled the Automatically Delete Historic Case Flags History Tracking Records setting under the Case Flags History Tracking section in the Case Flags Setup Wizard. However, if you need to perform a manual clear of the Case Flags History Tracking Records, review the following options.
Create a tab for the Case Flags History Tracking Custom Object that comes packaged with Case Flags, so you can easily access the records.
Go to Setup - Tabs - look for the Custom Object Tabs section - click New. Follow the steps until completion and then easily access the newly created tab from the App Launcher menu.
Access the list of Case Flags History Tracking records by pasting this to the end of your Salesforce Org's URL: /lightning/o/FLAGS__Case_Flags_History_Tracking__c/list
The URL as a whole should look like this: https://xxxx.force.com/lightning/o/FLAGS__Case_Flags_History_Tracking__c/list
Create a new List View to display all records.
On a Case per Case basis, make sure that the Case Flags History Tracking Related List is added to the Case Page Layout, locate it and open each Case Flags History Tracking record individually.
You will see a Delete button at the top right corner.
Use Data Loader to mass delete records. More information here: https://dataloader.io/deleting-data-salesforce
Note: in order to delete Case Flags History Tracking records, users need to have 'Delete' permission on the Case Flags History Tracking custom object that is packaged with Case Flags.
More information here: https://help.salesforce.com/articleView?id=sf.basics_deleting_records.htm&type=5