To add contributors to a liveblog, you need to have invited users to join your team and be on a plan other than Trial.
Step 1) Adding someone to your team
This step can only be done by an Admin User - the person who manages payment of the account.
To invite users to join your team, ensure you've upgraded from Trial. Then navigate to the Manage Team section on your Account page.
Enter the email of the person you wish to invite, and have them accept the invite via the email that has been sent to them. If you've run out of invites, you can either upgrade your account for more, or contact support.
Step 2) Inviting team members to contribute to a liveblog
Once they've accepted the invite, they will be associated with your team and plan permanently.
To add a team members to a liveblog, navigate to an event console and select the Contributors tab. You'll then be able to invite your team members to join you.