On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough of the Bridges of Oppression side quest.
Reward for completing the mission: 1200 XP.
In the place marked in the above picture, under the bridge, you will meet a crying man who will ask for help. When you ask what happened, he replies that the man he works for accused him of thievery and blinded him.
The victim will not be able to move, so you will have to carry him to shore. Throw him on your back and jump on the drifting pallets and transport him to the other side of the canal. Take the man to the bridge and lay him on the ground and his employer will take care of him. After a short conversation, the quest will end.