"I am feeling really good," the 40-year-old mother of two told GMA colleagues Robin Roberts, George Stephanopoulos and Josh Elliot. "Physically I feel remarkably well. Mentally, it's another challenge."
Robach's breast-cancer diagnosis came after she took an on-air mammogram for the show's October Pink Initiative. The discovery shocked the correspondent, who has no family history of breast cancer.
She quickly decided to have a double mastectomy, and doctors ultimately discovered the cancer had spread to at least one lymph node. Robach, who is married to actor Andrew Shue, will begin chemotherapy Dec. 16.
Throughout her homecoming appearance, Roberts credited cancer survivor Roberts as a role model for facing her continuing health battle with a positive outlook.
"I'm going to work through it," Robach says. "I saw Robin do it. I know how strong you were. And you give me strength, Robin, because it is important to get up and have something to do each day ... even if you feel crappy."
Robach refers to her successful surgery as "step one" in her recovery journey, but knows that "the next couple of ones are going to be tougher" and knows the mental toll will likely be harder than the physical one.
"Robin, you gave me some great advice. You said, you've got to go hour by hour on this one, day by day. And what it forces you to do is live in the moment," she says.
Yet Robach admits that's easier said than done.
"If you look at the positive out of this, there are days where if you really start to let your mind wander, it's fairly devastating," she says. "But you keep your head together, you come into work, you hug your friends, and you're thankful to be where you are with your family and the people who matter."
For much more on Amy Robach's decision to undergo a double mastectomy, and the battle that still lies ahead, pick up this week's issue of PEOPLE, on newsstands Friday