put https://mytenant.cx.onecloud.com/configapi/v2/scim/users/
Replaces all attributes of an existing user with a specified set of replacement attributes. Note that in accordance with RFC7644, the PUT method updates users by replacing all of their current attributes with the ones specified in the body of the method.
Note also that in order for usernames to be changed, service providers must allow this feature for your contact center. For more information, see the CX Administrator Guide, section Users.