ChatGPT is already available to users in the EU. It already has an EU-aligned terms of service. Not that I'd trust them, because the GDPR has been borderline useless in reality, but there's nothing particularly legally interesting about this offering.

> How do these EU citizens submit a request for all their personal data to be deleted from OpenAI records

Probably by sending an e-mail to a designated address, like most services that operate in the EU, but you can read their TOS if you'd like to be sure.