The workstation alias is intended to be a unique name to allow your Org's administrator to easily identify your workstation. Unfortunately when you install ArcGIS Pro, it does not default to the computer's name. Instead you have to start up the app, have a valid login to modify the setting.
In ArcGIS Pro go to About ArcGIS Pro > Licensing > Workstation Alias and then click Edit.
Or, just edit the registry. Changes will take place after you restart ArcGIS Pro.
Registry: HKEY_CURRENT_USER\Software\ESRI\ArcGIS Online For Pro\SignIn\SessionName