To set up the KORG SDD-1200 as a PingPong delay, the 3-Point Auto-Pan setup on page 12 of the owner´s manual is a good strat, but it needs some adjustments:

Korg SDD-1200 PingPong Delay

The source signal goes into unit A IN. Connect unit A EFF output to unit B IN. Unit B EFF output goes into unit A feedback input (F.B. IN). Connect unit A +MIX output to the left and unit B +MIX output to the right return bus input.

Set time and factor of both units to the same amount. Keep unit B feedback at zero. Adjust overall feedback with unit A.