The only thing that should need adjusting is the centreboard brake which is the rubber tube with a metal plate over it and two screws. This can be done on the water with the board down, though I guess if you tip the boat on it’s side you can do the same. You will need a long philips screwdriver. We had the opposite issue with our boat in that the board was too loose, so needed tightening.
If it is not this, then somebody may have over tightened the bolt that holds the centreboard in place. I have found Hartley’s very helpful so a call to them might help. Or see if you can find anything on Wayfarer centreboards as the set up is identical.