If the company that makes the panel still exists (which I guess they do), you could give them a call and explain the situation. They may be able to advise you, but be warned, many companies won't help people who aren't registered as installers.
If it were me, I'd be looking to make a note of which zone does what and then I'd go for a hard reset on the panel to restore factory defaults and then I'd reprogram it.
Failing that, engage the services of an alarm company to reset the panel and reprogram it, ensuring they provide you with the code. For an idea on cost, if someone asked me to do this, I'd probably be looking at around an hour.