The Live Room user permissions are based on the ‘kms Contextual Role’ which is related to the Media Gallery permission. If a user it set to Manager or Moderator, they will be Hosts inside the Live Room. In your LMS, this role is linked to the user's LTI role. In your LMS-Kaltura LTI setup, Instructors are usually set as ‘Managers’ and Learners as ‘Members’. You can check this in the KAF Admin LTI role mapping page.
In MediaSpace, there are two places to create a Live Room. You may associate a Live Room with a channel or a personal room. If associated with a Channel, Channel Owner and Managers will automatically be made Hosts. For an overview of how this works in MediaSpace, see Configuring Live Rooms in MediaSpace.