I want to download pro or core old version,how to download it?
Don't they send an email with your installation key and download URL?
Try this from the Zorin website:
In the case of Pro, yes. If a user wants a copy of Zorin OS 16 Pro, they need only reference the confirmation email from the ZorinGroup from when they chose Pro.
If they deleted that email, they can request a new link be sent: