First of all create the stitch in Stitch composer. (Or are you using my french knot that I gave the group? If so save it on your computer where you know where it is!)
Then copy it onto your usb into the Ordf folder. (If you're creating the stitch yourself this is where you also save it, in the ordf folder.)
At the machine:
Decorative Stitches: Created Stitches
Touch the tab for bringing a design into the machine:
The Usb will open, find the stitch and select it.
The Stitch will now be in the Created Stitch section of the machine until, if ever, you delete it.
To delete a stitch, First touch the trash can button, then the stitch you want to delete.