Starting with the release date of Endless OS 3.8.7, User can reset their user password over the online Password Unlock Tool web service.
This is a preferable way for the user with another device connected to the Internet to recover your access to your local account.
For more details steps please refer to his page:
Password reset through online self-service
This method is for users familiar with Linux commands. Begin with Endless OS 2.6 users are able to use an Endless-only command to reset their local account.
For further information on this tool and steps, please go to this page:
Password reset with command line tool