Activate Rookie Hunter mode at the game select screen or by using the Collection Menu while in-game (Tab on a keyboard, Select or equivalent on a controller).
Then you just need to fall into a pit while playing Mega Max X6.
For example, you may simply choose to start a new game, play the intro stage until you see some giant drills that come from above.
Let it destroy the platform below and jump down the pit.
You're going to respawn right next to it.
Mega Man X6 is infamous for its numerous bottomless pit, so this achievement makes a point to show "See? It's not that much of a problem anymore, stop complaining".
BEWARE: Activating Rookie Hunter mode, even if just for a second, will make that save file unable to receive some achievements, like the one from beating the game.
That's why I recommend doing it on a save file, or after you've acquired every other Mega Man X6 achievement.