
15 answers
I faced the same issue. You can not change the password for SSO users using workbench. The solution is to uncheck the permission "Is Single Sign-On Enabled" on the profile level withing the sandbox enviroment and then you can reset the user's password or change it directly through the workbench tool. Then the users are able to log in sandbox using the username and password.
You can also uncheck the "Disable login with Salesforce credentials" on the single-sign-on settings, then will be SSO disabled for all profiles.
Thanks to @Caitlin Marshall and @Svetlana Naibok for the ideas.