Account not showing previous purchase so can't download or upgrade

I’m sure there’s an easy solution to this but I haven’t managed to find it. Any help gratefully received!

I purchased Dorico Pro 2 in 2018 and installed it on my Macbook. I recently got a new iMac and decided to pay for the upgrade to Pro 5. Today is the last day of the activation window for that license but I can’t make use of it as my Steinberg account doesn’t show the Pro 2 purchase for me to be able to download it on the new machine and then make the upgrade. I could do with someone talking me through the process as I’ve already spent a few hours following various instructions and getting nowhere.

You probably already know this, but just to be clear - this process is complicated by the fact that Dorico licences in v3.5 and earlier used the eLicenser system, and Dorico licenses from v4 onwards use the Steinberg Licensing system. This means that when you upgrade from v2 to v5 you will need to use both systems. The Steinberg Licensing system is where your new licence will be, but in the old eLicenser system you will also need to go through a one-time step to mark the old licence as having been upgraded.

I think the instructions you want to follow are here: https://helpcenter.steinberg.de/hc/en-us/articles/4414539809426-Steinberg-Licensing-Upgrades-from-eLicenser-based-products