Damage party inside a script

[ShiningSword]

Hey, I'm using a leader swap script, and I wanted it to damage the entire party whenever they swap...
But I don't know howto do that inside a script...
Someone help me please

Here is the code

class Game_Party
  def shift_forward
    @actors << @actors.shift
    $game_player.animation_id = 16
    $game_player.refresh
  end
  def shift_backwards
    @actors.insert(0, @actors.pop)
    $game_player.animation_id = 16
    $game_player.refresh
    end
  end

class Scene_Map
  alias_method :seph_partycycling_scnmap_update, :update
  def update
  if Input.trigger?(Input::CTRL)
  unless $game_system.map_interpreter.running? or
  @move_route_forcing or $game_temp.message_window_showing  
      $game_party.shift_backwards
    end
  elsif Input.trigger?(Input::ALT)
  unless $game_system.map_interpreter.running? or
  @move_route_forcing or $game_temp.message_window_showing 
      $game_party.shift_forward
    end
    end
    seph_partycycling_scnmap_update
  end
end

*Script made by SephirothSpawn, minor edits by me