Easiest way is to use the standard customer service access points -- same path as the submitting a complain and provide as enough specific information about the individual as you can. Also avoid suggesting the employee broke any UA policies. Appears you have sent the basic info via that path already.
As for getting a specific gift / package to the individual. That gets a little more difficult. The Help Desk individual may or may not be an office worker vs at home employee miles away from any UA office. And airport agent is a little easier to get an item to since they have a physical work place.
A little googling suggests
Mailing address for United at EWR is
United Airlines, 1 Newark International Airport St, Newark, NJ 07114
You might try 973-242-0617, 973-623-0012 to see if they offer a better option.
Mailing address for United at IAH is
United Airlines, George Bush Intercontinental Airport, 2800 N Terminal Rd., George Bush Intercontinental Airport (IAH), Houston, TX 77032
(281) 233-0281