If the voltage is too high it usually can be corrected by reconnecting the primary taps on the transformer which feed the system. It is common for transformers to have +(2)2-1/2%FCAN (full capacity above normal)and (2) or (4)2-1/2% FCBN taps (full capacity below normal.)
Taps would be +5%, +2-1/2%, 0%, -2-1/2%, -5%, -7-1/2%, and -10%.
490v is very close to 2-1/2% high so reconnection of the primary tap to the +2-1/2% position would bring the secondary voltage to slightly below 480v. Remember that a transformer does not regulate and the voltage often varies as the load changes. And also the utility supply voltage may also especially at different times of the day.