Would be better if you can isolate it to groom it back to health before returning it to the tank.
There might be internal infection affecting its eating, reason behind the spitting of swallowed food. Arowanas dont try to swallow things it dont want to eat. I guess this fish wants to eat, but some irritation is causing it to spit the food.
isolate it in a tank with clean water and lots of aeration. try to deworm it with some of those products out there. eg, those deworming products for rays.
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