We recently purchased a set of Deco P9 as our internet was really poor around our house. Initially they all set up really quickly and were great. Then after a week the internet was dropping off my laptop so I pressed the reset button on the main Deco unit. Since this time about a week ago I have not been able to connect to the deco units. We have fibre to the property so I have disconnected the battery backup in this as well as waiting 10 minutes before reconnecting, swapped the units around   No joy what ever we do to reset up the blue light on the deco unit flashes and the app says that it cannot find the deco unit. 
 

I'm not a tech person in any way. Any help appreciated. Simple format please. 
 

Thanks