You don't need to create anything to move the origin other than typing numbers in the dialog box. Shifting the origin to the corner was a X-2. & Y2. move. To move it back you are now moving X2. & Y-2.
If you are moving back to the center and don't feel like measuring distances, just Alt + Shift (or Alt + click to load individual boxes) the geometry at the far end to load the value and add an operator (xx/2)
When I start a program I always rename Workgroup 1 to "reference" and use that for the sole pupose of creating reference geometry. I'll create a point here at XYZ zero and use that if I move the origin and need to move it back to this position.