How to get A Plague Tale Requiem without dying - guards at the docks

To avoid killing the guard at the docks during Chapter 4, you must:

1. Wait for the soldier to come down the stairs at the end of the level.
2. When he stops, use your sling to shoot the igniter in the chest.
3. This will set his clothes on fire.
4. Shoot Resin Stone at the chest with your sling to increase the burning and brightness and get rid of the rats.
5. Run past the disoriented soldier and go through the door on your left.

As you can see, the way to get this trophy or achievement is not the easiest. But in practice, this is not at all difficult to do.