On the left side menu, you will find a link to "Organization". Here you can set up your organization structure and also add and manage users for your companies. Keep in mind that this section is only available to user roles: Manager & Owner
On the top select tab "Users". On master company level here you will have a full overview of all users and what companies they are assigned to.
Click on +Add to add a new user
Enter the First & Last name of the user
Enter the users email address
Enter the phone number
Select a role, you can read all about it here: https://intercom.help/green0meter/en/articles/6217701-user-roles-permissions
Select all companies this user should be assigned to
Once a user is added you can edit the following fields:
First & Last name of the user
User role
Companies this user should be assigned to