code: def update_user(self, update_context, user_descriptor):
          
          route_values = {}
          if user_descriptor is not None:
              route_values['userDescriptor'] = self._serialize.url('user_descriptor', user_descriptor, 'str')
          content = self._serialize.body(update_context, 'GraphUserUpdateContext')
          response = self._send(http_method='PATCH',
                                location_id='005e26ec-6b77-4e4f-a986-b3827bf241f5',
                                version='5.1-preview.1',
                                route_values=route_values,
                                content=content)
          return self._deserialize('GraphUser', response)
docs: UpdateUser.
          [Preview API] Map an existing user to a different identity
          :param :class:`<GraphUserUpdateContext> <azure.devops.v5_1.graph.models.GraphUserUpdateContext>` update_context: The subset of the full graph user used to uniquely find the graph subject in an external provider.
          :param str user_descriptor: the descriptor of the user to update
          :rtype: :class:`<GraphUser> <azure.devops.v5_1.graph.models.GraphUser>`