The walls of The Bulwark have finally come crashing down. It is time to do some work for the people inside. A squad of Tenakth was posted at the watchtower. You need to be kind and go call them back home before they freeze. Here is how you complete the Call and Response errand in Horizon Forbidden West.
You will unlock this errand immediately after completing the Kulkrut story mission. Once the mission is complete, head back up into The Bulwark and talk to Gerrah to get the quest. Your first step will be to go to the watchtower at the Cold Rushes. It is to the west of The Bulwark. Follow the western path and it will lead directly to the watchtower.
After reaching the watchtower, talk to Kivva. She will be ready to head back but one of her people is stationed at a different watchtower. Go to the other side of the ravine and climb the rocks up to the other watchtower. Pay attention to the markers on your way up. They will guide you. When you reach the top, you will need to deal with a few Skydrifters.
After dealing with the Skydrifters, you will find the dead body of Kivva’s companion next to the tower. You will hear Kivva sound an alarm. The other watchtower is under attack. Jump from the watchtower you are at and glide down to Kivva. You will have to fight four Glinthawks. Afterward, talk to Kivva to complete the errand.