DuckDuckGo finds sites automatically, so there is no reason (or place) to submit particular sites or URLs.

Because we generate results using a variety of sources, information on our site is generally flowing from one of those sources. If it is in our Instant Answer box, you can identify the source by looking at the More at link within the box. It is best to correct misinformation at the source so that it will automatically flow to us and all the other sites that consume the source.