Turn a list of to-do's in Notes on my iPhone into a checklist

I read on your site that I can hit the "+" sign on the bar above the keyboard. There is no "+" symbol. Instead, above my keyboard is Suggested words "I", "You", and "I'm" above my keyboard.

I have an existing list in notes that I would love to be able to highlight and change it to a checklist rather than just a list.

Help please.

Thanks much.

Moe