From the Super Mario Wiki
A Goomba button is a numbered button in the shape of a Goomba appearing in Super Mario Odyssey. It can only be pressed by standing on it as a captured Goomba Tower consisting of at least the amount of Goombas indicated by the number printed on it. After activating a Goomba button, a Power Moon appears.
Three Goomba buttons are found in the game: two in the Snow Kingdom, and one in Bowser's Kingdom. In the Snow Kingdom, the first Goomba button is located in the Icicle Cavern and requires four Goombas to be activated to reveal the "Ice-Dodging Goomba Stack" Power Moon. After climbing higher in the cavern, the second Goomba button can be found, which requires ten Goombas and reveals the "Stacked-Up Ice Climb" Power Moon. This Goomba button only appears after breaking the kingdom's Moon Rock. In Bowser's Kingdom, another Goomba button that requires ten Goombas is located behind the right wall past the starting gate, which reveals the "Stack Up Above the Wall" Power Moon.