Reset alarm?

Hi,

Recently moved into a new house with an Accenta G3 alarm. There is what seems to be a panic box on the wall of the upstairs landing with a plastic key on it. Through curiosity/stupidity it was turned and the alarm system noise and light went off for approx 40 mins.

Can anyone tell me how to reset the alram system?

(Currently there is a blue light flashing every 5 seconds on the alarm box on the front of the house.)

Please help!

Thanks in advance