Dealer job I'm afraid - or someone who knows about mileage correction.
Had the same problem say 8 years ago. Changed the instrument cluster and odometer would not increase - the flashing was there too. I drove for about 6 months until I could afford to get it put right. The BECM had been calculating the 'real' milage and so after a visit to the dealer I had about 8,000 extra miles (that I had really driven) added to my odometer.