When viewing the item in your kit list, select "Options" then "Add NFC".
Tap your phone against the tag. You might have to find your phone's NFC "sweet spot". This is usually along the top of your phone, sometimes toward the top back or top front. It can take a little patience trying to figure out exactly where your phone's NFC antenna is, but once you've got it, you're sorted!
For more info on our NFC Tags and how to apply them, check out this blog post.