The feature to reset a user password is still in development and it will be available in the next official release of Telerik Report Server. The reset operation will be handled via e-mail (if an SMTP server has been configured).
At the moment, you can reset the password by erasing the storage data of the Report Server. You can do so by deleting the contents of the C:\Program Files (x86)\Telerik\Report Server\Telerik.ReportServer.Web\Data folder.
Let us know if you have any additional questions.
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