1. I presume that you have taken care of the $30 and any associated administrative fees.
2. Write to Hertz, simply advising that with the passage of time, you would like to be removed from its DNR list. Keep the note to 2-3 short declarative sentences.

As fair warning to others, rental companies are particularly intransigent on unpaid balances, chargebacks, and other similar items. Think carefully before taking action.