code: def change_axis(self, axis_num, channel_name):
          
          current_channels = list(self.current_channels)
          if len(current_channels) == 1:
              if axis_num == 0:
                  new_channels = channel_name,
              else:
                  new_channels = current_channels[0], channel_name
          else:
              new_channels = list(current_channels)
              new_channels[axis_num] = channel_name
  
          self.set_axes(new_channels, self.ax)
docs: TODO: refactor that and set_axes
          what to do with ax?
  
          axis_num: int
             axis number
          channel_name: str
             new channel to plot on that axis