ride it. 4-5mm is not that much, if the bike is already built ride and see if it tracks OK. if there are issues perhaps there is someone near you willing to help. there is some home method using string but I never tried it and would not recomend to a newbee.
what kind of brakes? there should be flats on the back side of the centerbolt so you can use a 14mm (maybe 13) come wrench to center them on the wheel
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk