To learn how to tame Blood Beasts, you must obtain a Blood-Soaked Tome of Dark Whispers. This book is a guaranteed drop from Zul in the Uldir raid on Normal Mode or above (i.e. not LFR). Once you learn the tome on one hunter you can tame Blood Beasts with any hunter on your account.
The corrupted spawn of the toad loa Krag'wa, perhaps you can redeem one of these ugly beauties!