Anybody who is concerned and wants to learn what personal info of them ticketmaster holds and hence may have been compromised, and lives in a country where GDPR applies, they can send them a GDPR subject access request, eg something like [0]. Their emails in general look like privacy@ticketmaster.XXX where XXX the country code but probably also double check to make sure.

[0] https://www.linkedin.com/pulse/nightmare-letter-subject-acce...