a.js

const graphql = require('@octokit/graphql');

const a = async () => {
    const query = `
      mutation {
        addLabelsToLabelable(input: {labelIds: ["MDU6TGFiZWwxMTY1MDg0MTQy"], labelableId: "MDExOlB1bGxSZXF1ZXN0Mjg4MzIzNzcz"}) {
          clientMutationId
        }
      }`;

  const foo = await graphql(query, {
    headers: {
      Accept: 'application/vnd.github.hoge-preview+json',
      authorization: `token xxx`,
    },
  });

  console.log('foo: ', foo);
};

try {
  a();
} catch (err) {
  console.log(err);
}