On this page of guide to Assassin's Creed Valhalla Wrath of the Druids, you will find a detailed walkthrough of the main story quest War Efforts.
With Ciara's help, Eivor tries to get support from surrounding kingdoms to bolster Flann's army.
Reward for completing the mission: 300 XP.
Speak to Ciara
From your conversation with Ciara, you will learn that you need to complete several smaller tasks for the rulers of the surrounding kingdoms. In return, they promised to send their soldiers to reinforce Flann's army.
Gain support from Meath's kings
Approach the nearby Pigeon Coop and check the requests of the Kings of Meath. You must complete three assignments to move on to the next stage of this quest.
Note that the tasks can be of different nature, but usually they're related to eliminating bandits or stealing certain items. If you manage to complete the assignment by observing all the guidelines, you will receive a small bonus.