Basically when you start volcano approach the game will try to teach you how to dash, but you're gonna shoot the flying inks to the right until you get the achievement, they'll respawn so you can repeat again if for some reason you don't make it

I wanted to make this guide 'cause I was genuinely struggling to get inkinator and the only achievement guide I found doesn't explain further like this so I leave it here so someone can get this achievement more easily