What he's saying is that there is a video showing u how to reset the code on texecoms own youtube channel. Not very professional behaviour if u ask me.
You will need to identify the wiring for the zone that has been removed and disconnect it from the global tamper circuit. Assuming this is the only tamper fault currently present then the system should then reset.
Have u put the lid back on the control panel? May just need reseating. So the spring is depressed. Yes it will need to be reprogrammed if codes have defaulted then everything else will have too. And a new battery as above
Probably best off asking whoever required the house, could be anywhere lol. But presumably would have been wired to the location of the router at the time ??