Collider Gizmo
For more information about the collider of Cocos Creator 3D, you can read the Physics Introduction documentation.
Box Collider
Box Collider Gizmo
shows the length, width, height of the box. You can edit them by dragging the control quad.
Sphere Collider
Sphere Collider Gizmo
shows the size of sphere, you can edit the radius of sphere by dragging the control quad.
Continue to the Scene Editor documentation.