Refine a selection
Zoom in, erase unwanted areas and save a clean cutout.
Inspect the cutout
Open Selection to see your subject on a checkerboard background. The checkerboard represents transparency and is not part of the exported image. Look at the edges, gaps and thin parts.
Use the eraser
Activate the eraser and choose its size. Use a broad brush for large unwanted areas and a smaller one near the outline. Undo a stroke if you remove too much.
Work closer
Zoom in to inspect small details. Turn off the eraser to move around the zoomed image, then return to the full view to check the overall silhouette. To add a missing part, return to Photo and use Add to mask.