Clean reinstall of CiviCRM Extension GDPR on Wordpress
Taken from a comment by @ParvezSaleh

The extension does not remove the custom data or activity types when uninstalled. This is a deliberate feature as it's assumed that any data collected to date is important and would be required if an audit takes place. 

It would therefore be necessary to manually remove the information from the database.

The extension's settings are stored in the civicrm_settings database table as a record with name set to gdpr_settings.

Other information (activities, custom field data) are stored in various database locations including civicrm_activity and civicrm_value_sla_acceptance_N (there may be other locations.)