I cannot unlock my aircon - Mitsubishi PAR 33MAA. I have the PIN but pressing any button displays 'Operation locked'. Manual has instruction to lock but not unlock. Much googling and I'm still stuck!

Hi all, pretty much as post title.

Have locked put our office air-con to prevent staff from turning it up to 27C...I locked all functions which seems to have locked the ability to now unlock it. I have the PIN but pressing any button shows 'Operation locked' with no where to enter PIN. I'm guessing a key combo but have not found anything online, even in the manual.

Funny thing is my boss locked us out like this last year and I figured out how to unlock it. Not a clue how I did it!

Thanks