TL;DR: We're given the source for a Turing machine, which has four main subroutines:
* Converting ASCII to binary
* Checking that the input has the UMASS{} flag format
* Swapping pairs of consecutive bits
* Left rotating the tape
taking the output and applying these operations in reverse order gives the flag.

Original writeup (https://bburns.xyz/blog/umassctf2024.html#primitive-reversing).