You'll always have unlimited access to download all paid projects sent for editing.
If your Lightroom catalog has not been moved from its original location (where it was when you uploaded the project), it will automatically load when selecting the project.
If it has been moved from that location, you can use the 'Browse' button to locate the relevant Lightroom catalog."
The Lightroom catalog doesn’t have to be the same catalog. As long as it has the original images sent for editing and the same folder structure, Imagen will have no problems downloading the edit.