try feeding it bloodworms. If it accepts them, then start mashing in a bit of pellets into the mix. Increase the amount of pellets everyday gradually over 2 weeks. Eventually you should end up with a thick paste. At this point it should already be used to the taste of the pellets, but not the texture. So start adding in whole pellets in with a bit of paste. When feeding the bloodworm/pellet mix to the arowana use a spoon and only put in what it can eat in one bite at a time. Also feed in the same spot. This is the method I used to pellet train all the peacock bass, silver aros, jars ive ever owned.