This is part of what I have to cover in my OSSLT (literacy) course.
It walks them through how to write a reflective paragraph.
-what reflective writing is all about
-the prompt - writing about a mistake they've made
-an explanation of the two paragraphs they have to complete, and what needs to be included in each of those paragraphs
I always keep good examples of these to read to them - not only because it's good to show an examplar, but also there's LESSONS involved in this style of writing.
TIP - to get them unstuck, I do a "free write" minute - where I time them for a minute, and they wrote a point-form list NON-STOP about "regrets in your life"
-This activity kicks their brains! Gets them brainstorming