There are two main methods of performing Doplieren - the "early" period version and the "late" period (Meyer) version.
The early period version of Doplieren is shown in sources such as Pseudo von Danzig and Ringeck. When two cuts meet (two Oberhauw/Zornhauw style cuts, for example) reverse the blade over and behind the opponent's by pushing the left hand/pommel under the right arm. Immediately cut behind their blade with a short mittelhauw or zwerch to their face with the long edge, typically cutting to the right opening and keeping the cross guard well up and in front to protect the head.
Meyer's doplieren differs slightly from the previous version. Instead of crossing the hands and cutting straight behind the blade, Meyer uses a flicking (Schneller) action with a move to your right to cut a Sturtzhauw or Krumphauw type of action to the opponent's upper left opening. In this respect it greatly resembles a blind strike in some ways (Blendthauw).
See Zornhauw Application - Doplieren