Since the instruction says "helpful piece" — if this is from a puzzle, the answer might be a word or phrase like "helpful piece" itself, meaning the decoded string is helpful piece .
Given the context ("helpful piece"), maybe it's just a that decrypts to something like "this is a test" or "helpful piece". dghlcmugaxmgbm8gag9wzq
If you intended a simple Caesar shift: Try shift of 5: d(3)→i(8), g(6)→l(11), h(7)→m(12), l(11)→q(16), etc. — but that doesn't produce English either. Since the instruction says "helpful piece" — if
Given the symmetry, I’d guess the is that after applying Atbash, you get welcome to the puzzle or similar, but my quick attempt didn't yield that. dghlcmugaxmgbm8gag9wzq