private void rollbackPrepareMerge(final MasterProcedureEnv env) throws IOException {
    for (RegionInfo rinfo : regionsToMerge) {
      RegionStateNode regionStateNode =
        env.getAssignmentManager().getRegionStates().getRegionStateNode(rinfo);
      if (regionStateNode.getState() == State.MERGING) {
        regionStateNode.setState(State.OPEN);
      }
    }
  }
Action for rollback a merge table after prepare merge
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/MergeTableRegionsProcedure.java