This is with nova launcher prime.
1. Select the folder you want to change the icon for. In this case I'll be changing the camera folder icon.
2. Long press the folder and you will be given a list of options
3. Select edit and these options will come up and you want to change the icon for the folder, select the picture of the folder.
4. You will then be taken to your installed themes. You can select an icon from your themes or swipe all the way to the left to get to your gallery and use your own icons.
5. Select your icon. I've selected this icon for my camera folder. And as you can see I've given my camera folder a name.
6. Select the checkmark in the top left corner of the Window when you are finished editing this folder icon. That's it. You've now customized the look of your folder from a preview layout to a single icon. In the second picture you can see that when the icon is selected it opens your folder. Done.
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