I guess you have a styrofoam core. This foam is nasty when it comes to remove water.
What I would suggest. Find yourself a frigde motor. You also will need a marmelade or pasta glass with a metall cap.
Two pieces of 6mm brass tubes, a little bit 5 minute epoxy and 6mm platic tube, tape and dark plastic foil, the darker the better,
a piece of thick clear plastic foil.
Drill 2 - 6mm holes in the metall cap. Glue two 6mm brass tubes in the holes. The glas will be the water trap. Slip the tubes
over the brass tubes.
Connect one -> pump to glas. Connect the other to the pump. Open the demaged part of the board. You have to repair it lateron anyway.
Now things get tricky. I don't know what type a material to seal the board you have in your country.
Sealing can be done either with acrylic or silicone, double stick tape. We have both, acrilic and silikon in plastic tubes 750ml.
Avoid if possible the use of silikon. Cover with tape widely the demmaged area with tape to prevent the "sealing" sticking to the board.
Add a track of arcilic rectangular around the demaged area on the tape. Fix the tube on the board so it will not pop of. Cover the end of the tube
with toilett paper, so the vakuum can not suck the foil in.
Place your clear foil on the acrylic track. Start the pump. Cover the board with the dark foil so it heats up. Let the thing run a week or
The only problem you will face is, if you use silikon for sealing. I any case prevent the stuff to get in contact with the board.
This technique is proven to work, but needs time to get the water out