I’m running CMX ver 10.3 and have locked myself out the gui ( graphical user interface). I do still however have access to the CMX cli and will demonstrate how to reset the specific user password through the cli.
In order to reset the gui password, you need to have access to the cli.
Step 1: log into the CMX cli.

In my lab, i only have one user setup on my cmx server and that is the admin user. you can confirm the users configured by typing the following command:
cmxctl users list
Step 2: enter command:
cmxctl users passwd admin

Hope this helps you!