More hvac questions. Lol.

I got an ecobee. And finally the transformer and relay I need to make it work with my old ass furnace came in.

So I can now have the furnace run when the upstairs is cold if the wood stove is off as well as if it gets too cold downstairs when the wood stove is on.
Other thing I’m wondering is there a way to also have the thermostat now control the fan alone. The fan will run when the furnace is on but if I want to only run the fan I have to hit a switch that is on the side of the furnace

I’m aiming I should be able to wire up a relay to have the thermostat control this.

Is there an easy kit for this?