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Quite apart from the problem of determining an exact date for this period (as Oldcat metioned in his comment), the details of the events concerning the suppression of the uprising led by Hunold (or Chunoald) are sketchy and probably spread out over a period of a few weeks at least.
The suppression of the revolt in Aquitaine was Charlemagne's first solo military action following the death of his father in September 768. We know that Charlemagne spent Easter 769 at Rouen on the way to Aquitaine. He requested the assistance of his brother Carloman to put down the uprising but the brothers fell out when they met up at Duasdives (Moncontour de Poitou, between Angers and Poitou) so Charlemagne continued alone and does not seem to have had much trouble dealing with the revolt. According to Roger Collins in 'Charlemage' Charlemagne took Angouleme and established a fortress at Veronicas on a tributary of the Dordogne. As
Chunoald was unable to put up any recorded resistance
it's hard to see what specific date the question might be referring to.
Next, according to Einhard, a Frankish scholar and courtier, Charlemagne forced Hunold
to abandon Aquitania and retire into Gascony, Even there he did not allow him to remain, but crossed the Garonne, and sent ambassadors to Lupus, Duke of the Gascons, ordering him to surrender the fugitive, and threatening him with war unless he did so at once. Lupus, more wisely, not only surrendered Hunold but also submitted himself and the province over which he presided to the power of Charles.
Nothing more is heard of either Hunold or his wife, according to T. Hodgkin in 'The Life of Charlemagne'.
Other sources:
Rosamond McKitterick, 'Charlemagne: The Formation of a European Identity'
Dale Evva Gelfand, 'Charlemagne'
http://fmg.ac/Projects/MedLands/CAROLINGIANS.htm#LouisIEmperorB