After you select the Spot Healing Brush, the Brush Picker drop-down menu appears in the options bar on the upper left-hand side of the screen. Click it to open the Diameter window. Drag the Diameter slider to adjust your brush’s size.
Choose a diameter that’s slightly larger than the goober you want to remove. As you adjust the slider, you can go back and hover your mouse over the goober to see how the brush’s diameter changes so you know when it’s big enough.