Since the regular AssetRegistry.bin (not DevelopmentAssetRegistry.bin, which is also saved by the cooker but not part of the package) is a copy of the one shipped inside the pak file you should be able to extract the AssetRegistry.bin from the pak files of your release and copy it into the Releases/<version>/ dir.
However, if you did not use “createreleaseversion” you are also missing the other files places in the Releases/<version>/ folder that is expected as an input here. I think the AR might be the only thing required for a patch, so restoring the AR.bin might already be enough in that case.
Here’s an example command to extract a pak file:
D:\Path\To\UE\Engine\Binaries\Win64\UnrealPak.exe -Extract "D:\ProjectName-Windows.pak" "D:\Outputfolder\"