How to add someone to the ADAdmin Role?

How to add someone to the ADAdmin Role?

I know I've done this when we first implemented the product, but now i can't seem to get it done.  I want to add another IT tech to the SDAdmin role.  If I go through the 'Roles' section it just allows me to view members of customize the role's rights.  If I go into the 'Technicians' section i can see a place under 'Select Permissions' to add the tech, but it wants a user name and password and won't proceed without it.  I don't know his AD password!  i don't want to know...what am I missing?
 
Thanks

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