Many times if I cannot immediately transfer a design [i.e. updating older phone cases that don't exist anymore, to newer ones that do], where you find a gamut of products to transfer - just not immediately to another phone case. You can copy and paste.
The old process still works, if traditional copy and paste doesn't work. The copy function appears if you right click on the design area. Open another product you wish to transfer it to, in a separate tab. On the new product, use the text box to add anything simple (i.e. an "a" or a "1"), then right click over the design area of the new product, and now the Paste will be there. Click paste and it should paste your design as a layer. Next, go back to delete the "a" or "1" text layer.
You've just copied and pasted your old design onto a new product.
