Difficult to answer with the limited information presented.
If the DNS of the domain is managed by dreamhost you can add custom DNS records via the dreamhost panel. Dreamhost generates a number of "non-editable" DNS enteries as you add specific dreamhost hosting services to your domain. For example: adding email services generates required MX records as well as DKIM and SPF records. It's my guess you want to change or add this type of record.