reset alarm?

If you are lucky, the original installer will have been an idiot and left the default engineer code in place.

Default Codes
Default User Code:
1234
Default Engineer code:
112233

All gleaned from a manual that took all of 30 seconds to find online:

http://static.premiersite.co.uk/24498/docs/1758647_2.pdf

https://www.chrislewis.co.uk/fireandsecurity/wp-content/uploads/sites/2/2016/04/Galaxy-2-Series-user-guide.pdf

HTH
August 2017