Nest thermostat heat source not functioning

[Tam5]

I have performed a factory reset on my nest thermostat a few times to change the fuel source from electric to gas. When I go to the nest app to change the fuel source the gas option is grayed out and I am unable to select it. I have had this nest thermostat since 2022. It normally works fine for heating the home, but now there's no heat just cool air. Any suggestions?

[CoolingWizard]

@Tam5 , using the Nest display go into SETTINGS and then rotate and select EQUIPMENT. Then select CONTINUE twice. Next, you will select HEAT TYPE, choose GAS, heat, and FORCED AIR. 

AC Cooling Wizard