1
Check the source
Confirm that the image is yours or that you have permission to modify it. Search for the unmarked original or an editable project file; either may be a better starting point than a flattened export.
2
Describe a narrow edit
Specify the marked area and the background that should continue through it. Ask the magic eraser to preserve nearby edges, color, and texture rather than changing the whole composition.
3
Inspect and compare
Compare the result with your saved source at normal viewing size and at full size. Look for repeated texture, a blurry patch, or a shifted horizon; return to the original if the reconstruction is distracting.