Some young people say 이욜~ instead of 와우(Wow!) as an exclamation when someone did a good job. For the answer for your question: "i didn't understand what you've just said, can you please write it (type it)?" Informal 방금 뭐라고 말했는지 모르겠는데 좀 써줄래? (between friends)

이욜 is came from 이야. we can use 이욜 like 이욜~~~~ 대단한데! / 이욜~~~~ 멋진데