To get it to heal, just get rare mushrooms, stand somewhere warm and eat a mushroom everytime the little plus signs are full. Resets the heal cooldown and your good to go.

if you use a syringe and drain your health to 10% or lower(without dying ofc lol), the pup will try to heal u aswell entering the state in which u can feed it

Found the tidepup on astreos on the new island if needed look on wikily for location info but idk if they r rare but can be found, i brought it to my base into a trap brought some dinos like otter and dodo and tamed it that way

You can injure yourself by getting bloodpacks and let it heal you for evolution progress. Its not hard but just takes a while, youre also working toward a bloodstalker while getting an evolved tidepup.

WARNING: if your tidepup cocoons itself it will lose all of its growth to evolve