There was a time when swapping seats in flight was regarded as a touch amusing, but as this was on a Tiger Moth I wouldn't advise trying it yourself.
One pilot would leave the front cockpit in flight and cling precariously to the wing struts as he fought the slipstream and stood on the walkway.. He could just lean into the empty cockpit enough to fly the aircraft via the control column. Meanwhile the other pilot would exit his seat and treading the wing walkway on the other side, clinging to everything within reach, ease himself into the vacant seat..The "Wingman" could then ease himself into the rear seat with the aircraft fully under control.
I heard that the advisory height for this seat change was above 1500agl...and yes...do wear parachutes!