The achievement requires you to complete the mission "Bury The Hatchet".
There is a video guide underneath the text guide if you prefer that specifically.
You can start this mission as Michael or Trevor. Once you start the mission, you will get a cutscene. After it, depending on who you chose to start the mission, you have to go to Sandy Shores Airfield for Trevor and the Los Santos International Airport for Michael, whoever you chose go to the location.Trevor
You will have to enter a plane and fly till you reach the yellow marker. In Ludendorff, North Yankton, you will be in the cutscene already.Michael
When you arrive, you have to go up a flight of stairs to get the cutscene. After it, you will be driving to the Ludendorff Cemetery. Once you arrive, go up to Trevor to start the cutscene.
After the cutscene, you will be Michael and have to fight your way through the cemetery. When you finally get to his car, it will go into a cutscene. After it, you will be Trevor and you will be tasked with flying back to Sandy Shores Airfield and landing on the runway. When you do, the mission ends.NOTE:
IF YOU DIDN'T GET THE ACHIEVEMENT WHEN YOU COMPLETED THE MISSION, IT MAY HAVE BEEN BECAUSE YOU SKIPPED DURING THE MISSION.NOTE:
IF YOU DIDN'T GET THE ACHIEVEMENT WHEN YOU COMPLETED THE MISSION, REPLAY THE MISSION VIA THE "GAME" TAB.
Here is the video guide.Michael
Credit for the video to GAMING BOTTENE ( https://www.youtube.com/channel/UCXxARCrM7MQft6ztaOqiU7g
Credit for the video to Spyirate ( https://www.youtube.com/channel/UC7dqeRf3ohLeFnyS3WwymGA