I did not make a withdraw on my HSA other than monthly fees. What distribution code should I use?

"What distribution code should I use?" Use on what? Did you receive a 1099-SA?

Monthly fees from an HSA are not considered distributions from an HSA. Did you receive a 1099-SA for your monthly fees? 

Fees that your HSA custodian takes from your HSA for their service are not distributions and are not reportable.  You only have a reportable distribution if you receive a Form 1099-SA and you would enter that form exactly as provided.