Welcome @molly7, I don’t know of any Lucid Dreaming apps for Apple devices. I typically use Android. I wanted to say hello 
& I hope you can find something to help you.
I believe we have done some other things on Lucid Dreaming as well:
→ 
Lucid Dreaming - How to Gain Control of Your Dreams
→ Learning to Have Lucid Dreams
→ Visualization: Crystals, Meditation, Guided Imagery - this has a link to crystals to assist with Lucid Dreaming & a little bit about lucid dreaming within it too!