How do i unlockm HMS

I got a wailord and i want to get waterfall on him, but it isn't unlocked. How do i unlock it?

 

Hi there, Mckenna! Sadly, the only HM that is currently unlocked is Rock Slide, which was used in the first Legendary Bird Quest, which is no longer available to do. I hope this helps, and feel free to contact me if you have any further questions!

 

Thanks and cute dog!