Segment how to track an event for a user which is not the current user

Need help Plugins
1

Hello, my problem is the following :

Note: I am using the Segment Bubble Plugin

  1. When a user signup a identifies him, it’s working perfectly

  2. When my user for example takes his first action and goes through onboarding, I trigger a server event with segment, which is also working fine

  3. If another user, for example, adds a review to my first user. I want to trigger an event to identify that the first user gets a review.
    But it seems that I can’t assign an event to a user which is not the current user.
    I don’t see an option to add the “User ID”.
    I can only add “traits” like email but they don’t seem to help Segment to identify the user linked to the event.

Thanks for your help!