How to use Relay updater function

MyComponent.tsx

const contentMutation = graphql`
  mutation MyComponentContentMutation(
    $postId: ID!
  ) {
    deletePostContent(postId: $postId) {
      id
      content
    }
  }
`;
const POST_ID = 'uniquepostid';
const MyComponent: FC = () => {
  const [deleteContent] = useMutation<MyComponentContentMutation>(contentMutation);
  const onClick = () => {
    deleteContent({
      variables: {postId: POST_ID},

      updater: (store) => {
        // Find the `Post` record of interest in Relay cache.
        const postRecord = store.get(POST_ID);
        // Update its `content` field to `null` if the record exists.
        postRecord?.setValue(null, 'content');
      },
    });
  }
  return <button onClick={onClick}>Delete Post Content!</button>;
};