I used [quipqiup](https://quipqiup.com/) to solve the challenge.

**the flag is: picoCTF{FR3QU3NCY_4774CK5_4R3_C001_7AA384BC}**

Original writeup (https://github.com/DoomHackCTF/WriteUps/tree/main/picoCTF2022/Crypto/substitution1).