When choosing who the default reviewee for a conversation should be, Klaus looks at the most active agent in the conversation.

So if the current assignee of the conversation in your help desk only responded to the customer once but another agent responded 10 times, Klaus will choose the second agent as the default reviewee as they are the most active agent.

If you prefer for the default reviewee in Klaus to be the same as the assignee in your help desk, you can choose this in your Workspace settings: