Since this guy got a tlc the new taming method will be by crafting an apex offering at lvl 96 which is made out of alpha creatures trophies then approach a wild one with the apex offering in your inventory it wil take it and accept your challenge I recommend using a High hp stego with a decent saddle then get the giga into its rage mode by damaging it if you want to fill more torpor, then let the giga attack you until its unconscious and take a bunch of narcotics or bio toxin to maintain its torpor and feed it exceptional kibble