If you signed up before Aug 9, 2021, please click Previous plans to view your applicable plans.
You would need the full XML export file from Zendesk. The .zip folder would have the following files - users.xml, tickets.xml, entries.xml, accounts.xml, organisations.xml, forums.xml, categories.xml, and posts.xml. Kindly provide these information to us by writing to support@freshdesk.com, we could have this imported into your account.
Apart from this, you could also install the Zendesk Migration app, from under Admin-->Apps-->Get More Apps-->Zendesk Migration-->Install. There, you could enter your Zendesk Account details, which would get migrated into your account, using the App.