Erase part of a drawn imge

You can easily do this for yourself – select the blue with the Quick Selection tool then Option plus Delete to fill the selection with the default black fill.

@snow37679556nt3y 

Try this:

Eyedropper tool: click on the black to sample the color

Brush tool: paint across the blue smudge with black

Are you using Photoshop for Windows or Photoshop for Web? You selected both as topics.

Jane