Hi @– Pem –:
To clarify, you are trying to add every occurence of the words Level 1 – Illustrations to your index?
You can use a variation of the technique described here: https://www.rockymountaintraining.com/adobe-indesign-index-all-occurrences-of-a-proper-name/
In your case, carefully index the first occurence. Update the index and make sure it looks correct. Then open Story Editor and copy the index marker and text to the clipboard. In the Find/Change dialog box:
Find: Level 1 – Illustrations
Change: Clipboard Contents
~Barb