I am upgrading to a new computer. With this move, I have taken the 1 TB hard "internal" hard drive containing my LR catalog and photos from my old computer and have connected it as an external hard drive on the new computer. My next move is to load Lightroom CC onto the internal drive of the new computer and remove the software from the old computer hard drive which is now just an external photo storage drive.
Then, the tricky part where I need help. How do I get LR to recognize the existing catalog on what is now the external drive?
You double-click on the catalog file to open it in Lightroom.
As DJ says, just double click on the catalog on the external drive.
Or, from the LR menu, /file/open/ and navigate to the external drive.
Either way, after opening the catalog, you will need to go to the Library module, Folders panel, and "find missing" on each top-level folders to tell LR that you move the folders to the external drive.