The wpcrm_system_gdpr_deletion_message allows you to modify the message that is shown to contacts when they request that their data is deleted.
By default the message reads:
Your data is marked for deletion. We will review your request and remove it from this site as soon as possible.
This message is passed to the filter and can be modified, or changed entirely. The message that is displayed should indicate to the user what will happen with the data that they requested to have deleted.