Copying Lr catalog to new computer when files are stored on external hard drive

I've recently shot about 10k new photos and stored them on a brand-new external HD that my iMac has never seen. The way my iMac Lr catalog is organized (and the way I'd like to keep it) is by folders that each correspond to an external HD. Since I was traveling while I shot these 10k new photos, I imported them to my LAPTOP Lr catalog (just added them, not copied the files, so they read as living in the new external HD). I want to copy the catalog and edits to my iMac. I have researched how to copy them to my "All Photographs" catalog. But I specifically want to keep them, as they're stored in my laptop, as a folder contained in the backup HD. But my iMac doesn't even have a folder for that new external HD. I realize this is a total newb question, but how the hell do I just get that new HD folder in my iMac Lr catalog with all the subfolders, etc. from the Lr catalog in my laptop. I've already exported the catalog and air dropped it onto my iMac. I just don't know how to properly import so I'm getting the exact same folders and sub folders on my iMac. Thanks for your help, I'm on a deadline and need to edit these ASAP!

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