Ok it’s quite simple. You can think of it this way:
-It’s a secret text encryption but in the very begining it was a simple text written in english.
-SO: try to find similarities between the new text and the original one such like the words lenght.
-Try to figure out some words matching the contexte and for exemple some words lenght.
Once done you’re almost done with this level cause all you have to do after that is figuring out the relation between the guessed words and there matching words.