Had fault code P0380 - Board Relay Tharmostat or preheat ecu.
Can anyone tell me what or where is the B.R.Thermostat?

Generic fault code P0380 = Glow Plug/Heater Circuit "A" Malfunction

There's a guide to dealing with glow plug problems here:

https://www.fiatforum.com/stilo-guides/151734-dealing-preheat-fault-message-stilo-jtd.html

This is for a Stilo JTD but I suspect it's a similar system on the Doblo.

Dave.