You could set another user with full admin rights, if you know their password. See config\alfresco\authority-services-context.xml. They should then be able to reset any password. If you do not know any password - you can configure authentication to allow regardless of password. See the authentication configuration docs. You could then login in as admin, no password, fix it up and then put all the config back.
You could fix up the MD4 hash held in the database for the admin user although you would have to unravel some hibernate stuff.
Archive: Alfresco Content Services / ECM
Archive content from 2016 and relating to earlier versions of Alfresco Content Services, Community and Alfresco One.