Use the Outline Tolerance slider to increase and decrease the number of outline control points available, between 0 (the minimum number of control points) and 1 (the maximum number of control points).

Hold Ctrl to drag the line (here shown in yellow) rather than the control points. To move the outline instead of the control points, hold Ctrl while you click and drag the outline. Create new outlines by dragging in an empty space within the Sprite - you can use multiple outlines in one Sprite

Do this multiple times to create multiple outlines on one Sprite (for example, a donut Sprite which has gaps inside the outline). This creates a new rectangular outline with four control points. To create new outlines, drag in an empty space within the Sprite. Drag this to reposition the control point and the blue square becomes a new white square outline control point, as shown below Hover over a white square control point, then drag the blue square to the position you want the new control point When you hover the mouse over a white square outline control point, a blue square appears on the outline. The white squares represent the outline control points - click and drag to change their positions Click and drag a white square outline control point to change its position. Control points are indicated by small squares. The control points are areas you can use to move and manipulate the outline. The outline is indicated by a white line. The Sprite Editor displays the outline and control points of the Sprite. With Edit Outline selected, click a Sprite. Use the Sprite Editor’s drop-down to access Edit Outline Click the Sprite Editor drop-down in the top left, and select Edit Outline. To access this option, select the Sprite and open the Sprite Editor (click Sprite Editor in the Inspector window). This feature is useful for fine-tuning the bounds of a Sprite, ensuring there are fewer transparent areas in the shape. Transparent areas in a Sprite can negatively affect your project’s performance. Use the Sprite Editor’s Edit Outline option to edit the generated Mesh for a Sprite, effectively editing its outline.

Unity 2d sprite editor package