Dghlcmugaxmgbm8gag9wzq Here

Alternatively, maybe it's + ROT13 or a keyed cipher.

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 . 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. Alternatively, maybe it's + ROT13 or a keyed cipher

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. — but that doesn't produce English either

If we try of dghlcmugaxmgbm8gag9wzq (not standard Base64 length, but padding may be missing), it doesn't decode cleanly.

Another possibility: (common for such puzzles):

The string dghlcmugaxmgbm8gag9wzq appears to be encoded, possibly with a cipher like Caesar cipher, Atbash, or Base64.