1) When you are in your dashboard, Go to Projects:
2) Find your design and check the box in the top left hand corner.
3) And then click on the folder icon on the bottom of the screen:
4) If you already have a folder created - select that folder and click Move to Folder:
5) If you do not have a folder created yet, click +Create New
6) Then add the name of your new folder and click ‘Add to New Folder’