This guide will provide you with the easiest method to finish all 10 waves and complete CALL TO ARMS in Red Dead Online.
The first thing you will need to do is join the Call to Arms: Blackwater mission and head to the following location on the map.
After that, climb the boxes to head up to the roof and equip your weapon. You need to aim the weapon to make your character walk slowly and then land on the thin wooden stick.
After that, turn into the first-person mode and head inside the attic there. Now you can target the enemies and no one will be able to target you.
If the enemies stop spawning, then you have to come out and kill one enemy outside. Then they will start spawning again. After that, you need to do the same process again to reach the attic. Complete all ten waves there to complete the mission.