Unlikely to cure but possible to TRY.
1) You could cover up the whole tank dark with light off for a period of time beside feeding, some tried say its help some say useless.
2) Transfer Arowanas into pond for few wks to mths for the eye to adjust back to its style (Not 100% cure but maybe 80%)
3) Operation may help, well I'm not sure whether this really cures it - unless if you really find droopy eye is a big issue and "expensive loz" . 80% to 90% cure
4) Put some ping pong ball floating on the surface of the water to let the Aro looks upward - or those Rear bicycle flicking light (Red Flicking type) place on top of the tank cover.
5) Remove Tankmate that always swim at the bottom.
6) Feed floating food (ip: BF or injet Air into MP or Pellet Food)
7) It could be the genes of the Aro's family and if its Genes nothing you could do even after Operation it will still return after mths.
8) Monitor your aro whether it normally swim CW or CCW in the tank, adjust your pump to make it swim the other way. (i.e- if it's swimmin' CCW, adjust your pump to make it swim CW) Here's
Japan explanation of aro droop eye..