Re: I have moved a folder with images to a different external hard drive. Lightroom 5 will show any image from that folder as missing of course. How do I tell Lightroom to look in the new folder?

Your term Gallery isn't something I'm familiar with. But a collection is nothing more than an organizing tool that displays images wherever they are located on your system. If you update the folder location it should impact the collection as well because the collection is pointing to the same images. The collection isn't another copy of the images.