At your card carousel, swipe left or right until you have the "Add New" Screen:
Once you have reached the template page, select more to place in your template code:
Once "More" is selected, Place the template in the field provided:
Once you have started typing in the code the "Select Custom Template" will light up., then select it:
Your custom template will appear in your template carousel for you to select and edit:
See this in action on our Shuffle by Elify YouTube Channel: