Open the Custom Physics Shape editor

To open the Custom Physics Shape module, in the Project windowA window that shows the contents of your Assets folder (Project tab) More info
See in Glossary, select the SpriteA 2D graphic objects. If you are used to working in 3D, Sprites are essentially just standard textures but there are special techniques for combining and managing sprite textures for efficiency and convenience during development. More info
See in Glossary you want to edit. To open the Sprite in the Sprite Editor window, in the Sprite’s InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
See in Glossary window, select the Sprite Editor button.

To open the Custom Physics Shape editor, in the Sprite Editor window, open the upper-left drop-down menu and select the Custom Physics Shape module.