alarm was going haywire no company name or number on the box Alarm was already fitted when we moved in?

How do i go about activating the alarm that is already in my house?

I just moved into a house that has an alarm system wired into it and everything. It’s a “magnum alert.” My question is how do i go about activating it? Do i have to go through the company that installed it or does that matter? Can i go through any alarm company? Thanks!