ZOOM has created a PDF that accompanies the FEB 2017 patches that they created for the B3n, which explains the whole process of downloading and installing new patches.
If Zoom or anyone else has created patches for the B3n and saved them in a PC file format with the .zptc extension, what you do is select all of the files you want to have ACCESS to loading on your B3n from the file folder containing those patches, and then drag-and-drop those .zptc files onto the right side of the screen in GuitarLab in the blue area under the heading of Patch Pool, with the PATCH icon highlighted in GuitarLab. Patch Pool doesn't show up if you have EFFECT highlighted.
When you drag-n-drop from the PC folder to GuitarLab, there will be a new folder created in GuitarLab's Patch Pool area, which you can rename by right clicking. If you click on this newly formed folder, it will drop down list all of the new patches that were dragged there. Then, you can individually drag them from the Patch Pool folder onto the right side of an Empty patch (locations in the higher patch numbers above 80 or so), and you're done. Repeat for however many patches you want to add.