Back door contact sensor not working

HELP !!! I have a Generation 1 security system and IV recently had a problem with the back door contact sensor not working saying it’s constantly offline.I tried everything to get it working but nothing workedSo today I removed it and tried to reinstall but I’m not faced with 2 issues, firstly in the menu in my app it’s saying “waiting to connect to a network”Secondly when I go into it and select “finish set up” to takes me to a page, getting started, that asks me to pull the tab on the back of the sensor but obviously that isnt there anymore as its not a new set upIt won’t let me do anything else so I’m stuck with it not workingPlease help