The Guest Relations offices at DTD are located in the Marketplace and in West Side.
The Marketplace location is between the Team Mickey shop and the Ghirardelli shop towards the Rainforest Cafe end of the Marketplace. This is a walk-up counter located inside between the two stores.
The West Side location is at the Pleasure Island end, just past the AMC Theaters. Walk straight down from the parking lot with PI on your right and AMC Theaters on your left and you will see it right in front of you. It is a white building that says "information" on it. This is a Guest Relations window like the parks have.
Hours can vary depending on season but generally are:
Marketplace Guest Relations Located next to Team Mickey
Hours: 8:30 a.m. - 11:00 p.m. Sunday - Thursday
8:30 a.m. - 11:30 p.m. Friday - Saturday
West Side Guest Relations Adjacent to Pleasure Island, near AMC Theaters
Hours: 9:30am to 11:45pm
Disney's Earport shops at MCO cannot activate vouchers. That must be done at a WDW Guest Relations location. All Guest Relations locations (parks and DTD) can handle any upgrades, adding of options, extending days, etc.