Click Origin
in the Create group on the Design tab.
The origin is created based on the following:
If one planar face is selected, the origin is created at the center of the face.
If two intersecting faces are selected, the origin is created with XY in the first plane, Y aligned in the intersection
of the two planes.
If three intersecting faces are selected, the origin is created with XY in the first plane, Y aligned in the second, and
Z placed at the intersection of the third plane with Y.
