Adding team members to Support System to assign categories to

Dear Support,

I am struggling to figure out adding a user as a team member to the support system plugin.

It is a multisite install and support system is network activated. The super admin is the only name available in the drop down. There are 33 users on the network one of which is an Administrator across all the 28 sites.

I may be losing the plot and the answer is right in front of me but I'm just not seeing it.

Could you please point me in the right direction.

My goal is to add a particular user (the Administrator across all the sites) as a Team Member so support queries falling within certain categories will be forwarded to him.

Thanks in advance.
Will

PS - the attached image highlights the single user available in the drop down.