Hello Liam McCann1
I’m sorry to hear that you lost the package that you bought for Windows Server 2019.
If you are referring to the installation media for Windows Server 2019, you can download it from the official website of Microsoft ((Windows Server 2019 | Microsoft Evaluation Center) Download an ISO file and use it to create a bootable USB drive or DVD disc.
Please Note: This link is to download Windows Server 2019 Evaluation. The trial period is 180 days, and you can activate it with the product key before the trial period ends.
If you are referring to the lost product key, try to find your product key by following this link: Find your Windows product key - Microsoft Support
The product key cannot be replaced. If you can't find it, you can only buy it again.
Best Regards,
Hania Lian