If you don't have a manual, there is one available at
https://www.jukihome.com/media/catal...ion_manual.pdf on page 84 & 85 of the pdf or 83 & 84 of the actual manual shows how to use a twin needle. The automatic threader and thread cutter can
not be used with the twin needle. I'm fairly certain that not all the patterns can be used with a twin needle. It looks like it will have a circle with a slash if the pattern selected cannot be used with a twin needle. Also it will need be set for the center needle position.