I have a desk from Dellonda and am happy with it, but my nephew has managed to lock the height controls! How do I unlock them?!

Good morning,
Please see the below instructions;

Locking The Desk

• The raise and lower function can be locked by pressing the "M" with the padlock until the blue light comes on.
• If you try to raise or lower the desk while it is locked the control panel will beep.
• To release the lock hold the "M" button until the blue light goes off.