Note that currently there is a bug that only Baltim raiders count as ‘Herald ships’ the larger ships do not.
Just stay in front of the D’D and wait for it to fire plasma torpedoes, and shoot them down until you’re done. I prefer to do Acamar system patrol for this kill the Mogai so that you only face the one D’Deridex. The Point Defense Console could be very helpful for this Endeavor. Other Possibilitys: Carraya System, Undine Assault Planetkiller at the end and Crystaline Catastrophe.