Several ways to send a CM Compliment:
Go to City Hall or Chamber of Commerce to do this in person. Doesn't matter which park -- as long as you specify what happened, where, when, etc., the CM Compliment will get to the right department/supervisor.
Go to the DLR webpage, scroll to the bottom, look for the Contact Us link. When you fill out the form, leave all your contact information in case someone wants to get back to you. And don't be surprised if someone does -- they often do call or email back. I always put "ATTN: CM Compliment" as the heading, to make sure my comment goes to the right place.
You can use social media, as noted above.
It can't hurt to use more than one of the above methods, if you really want to make sure that a special CM gets noticed. If you don't remember the CM's name, that's all right. Just be as detailed as you can be with date, time, location, general CM description, what happened, and how that affected your guest experience in the parks.
Thank you for wanting to recognize a CM for making the magic!