Heart of the City is listed as a charity at Level 23, 151 Queen St, in central Auckland, with a Google rating of 3.7. Its website is heartofthecity.co.nz, and it is generally known as the organisation that promotes central Auckland's business district, so check how it describes itself before you get in touch.
A good charity is clear about its purpose, who benefits and how money is spent. In New Zealand, registered charities are listed on the Charities Services register, where you can look up their purpose and annual returns. Organisations that promote a city centre often run events, visitor information and campaigns, so check their website for what is on and how to take part. Regulars follow the newsletter or social pages, which carry events and news, and ask directly if they want to partner, volunteer or promote an event.
For people who live, work or visit in central Auckland, Heart of the City on Queen Street is worth a look, and its Explore page is the best place to start.