There is a way!
If you look at its Pokedex data here, Emboar learns it at Lv. 1.
What that means is that you simply go to the Heart Scale lady (In a building to the right of the Mistralton City Pokemon center) and re-teach it via Heart Scale!
(+) Not re-teach it, sorry if this confuses you, it's just one of those weird moves you have to learn by Heart Scaling!