Use temp sensor to set virtual thermostat (current) temp

I'm remote from my Hub and can't see the exact rules I'm using*, but in general terms:

Create a Rule Machine rule like:

    Trigger (Temperature Changed) /* where the Temperature device can be the virtual "Average Temperature" device */
    send %value% to VirtualThermostat(CurrentTemp) 

For a better explanation, see: Simple Virtual Thermostat Temp updater
and Average All Device Driver

Also, the forum search interface does return lots of useful hits:
Search results for 'virtual thermostat current temperature' - Hubitat