You must learn the skill to tame Blood Beasts, which is taught by a Blood-Soaked Tome of Dark Whispers, a guaranteed drop from Zul in the Uldir raid on Normal Mode or above (i.e. not LFR). Once learned, this skill is account-wide.
Location & Notes:
Located in Blood Gate, Zuldazar. Bloodbelly Flyers with three different IDs may be found around the Blood Gate area. This ID is only used by a few stationary blood ticks on the ground.