Accidentally removed fields from form

On my website, I provide links to articles written on other sites. There’s a form that was developed for me to create those links.

I was getting annoyed at the constant “you’re going to lose updates” error message I’ve suddenly started receiving even when there are no updates, and in my annoyance, I clicked an up-arrow on one of the form fields, and now it’s gone and I can’t determine how to get it back.

is there an easy-peasy-do-this-to-undo-it method, or am I boned?

The page I need help with: [log in to see the link]