Unplug the appliance from the wall socket. Pull it out and lower the drain hose into a wash basin. Raise the hose again to stop the water flow. Continue doing this until you get all the water out.
Once you have the water out, try to open the door.
If it still won't open try pushing it then opening.
If this doesn't work, you'll have to take the lid off, reach down inside and find the lock.
It'll take a bit of working back and forth, up and down, but you need to snap this part off it's screws. Once you get it off the screws unhook it from the door latch.
You'll have to replace the door lock with a new one.
Easiest way is to remove the retainer from the front part of the seal, peel the seal back and reach in to the lock.
Hope this helps.