DIAGNOSIS The door lock mechanism is engaged because the machine still detects water in the tub or a safety interlock has failed.
FIX 1. Ensure the cycle is fully complete. 2. Run a drain/spin cycle to remove any residual water. 3. If the display is blank, unplug the machine for 3 minutes, then plug it back in. This often resets the electronic door lock. 4. After the reset, the door should unlock with a click.
IF THAT DIDN'T WORK A faulty door lock latch assembly (part # DD97-01457A) is a known failure point. It will require replacement.
HEADS UP Never force the door open. There is an emergency release cord behind the lower kick panel, but use it only if there is no water inside to avoid flooding.