How Do I Do That in Photoshop?

Erase Something If I Make a Mistake?

If you make a mistake while painting with the Adjustment Brush, just press-and-hold the Option (PC: Alt) key and paint over the area where you messed up. When you do this (hold that key down), you’re actually swapping over to a different brush that’s set up to erase the mask, and since this is a different brush, it actually has its own separate settings. Once you paint a stroke, you can then click on the Erase radio button at the top of the Adjustment Brush panel, and then set your Size, Feather, or Flow settings ...