https://f95zone.to/threads/rpg-maker-mv-cheatmenu-v2-0-2.12121/
Make a back up of your game.
1) Download the cheat menu from the link above, install it.
2) Open the game and load your save, press "L" and the cheat menu should pop up.
3) Select "switches" on the left side, then set Gurtak dead to false and Gurtak witched to true.
4) Talk to Gurtak at the orc camp(where u killed him).
5) Go back to the hut where u manage your tribe, the red flag should appear.
U can change the switches back to how they previously were after u have sent your tribe at the ambush location.