Hello, I'm afraid that the contemporary sources on the 9th century Vikings (Danes) are so much more chaotic that I cannot offer any additional information on "Harold the Dane" in question.

I summarized some basic information as well as relevant literature on the alleged settlement of Rollo in Normandy (and Normandy in the 10th century) before in: Charles the Simple and Rollo.

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First of all, "Harold"<Old Norse Haraldr are not so rare name among the Viking leader as well as the royal member of the Danes in the 9th century so that researchers often have difficulty in distinguishing/ identifying which Harald is found in the text (or whether they are single person or not) (Cf. Coupland 1998).

As I explained before in the linked thread, we also actually know much less on the early life of Rollo before his appearance of a few (alleged treaty) documents in the first decades of the 10th century. The tradition that Rollo firstly came to Normandy during the alleged reign of Charles the Bald (II) of West Franks (d. 877) dates only back to the early 11th century, in the hand of Dudo of St. Quentin's History of Normans (1010s?), so written about a century after the actual event, and it tells us very little about followers of Rollo. Some scholars also doubts the identification of the king (when Rollo first took a visit in Normandy) with Charles the Bald.

Thus, I have met difficulty in tracing this "Harold", OP's alleged ancestor, in contemporary sources, so far.

(Added): As for the latest research on the political history of Normandy in the 10th and 11th century (in English), Mark Hagger, Norman Rule in Normandy, 911-1144, Woodbridge: Boydell, 2017, is probably the most detailed one, but we cannot expect much descriptions on the political event in the 10trh century.