Brush Type Use the Brush to add brush strokes to the mask which is used by the Remove Object layer for the selection of the object.
Use the Eraser to erase brush strokes and deselect some parts of the object in the image.
Brush Size Use the slider to adjust the size of the brush when adding or removing selection from the mask.
Click to start removing the unwanted objects from the image by allowing AI to process the selected areas. Click Undo to make adjustments to the selection of the unwanted objects and try the process again if you don't like the result.
Note: The process might take some time to finish if the selected area is too big.