OK, all you need to do is find an ac adaptor. Anything from 5 to 12 volts
is ok. It must say Output: DC
The lower the voltage the slower the fan will spin. All you are trying to
do is move the air around.
Once you find an adaptor just hook the two wires of the adaptor to the
two wires of the fan. We are dealing with low voltages here so you
won't get shocked. Use electrical tape to insulate the wires. Duct tape
will work too.
You want the fan sucking in air on the side of the fan motor and blowing
out the other side. To change direction of the fan just swap the wires.
You will blow the fan up, not down. Blowing is up will move air somewhat
evenly around the bator. Blowing it down towards the eggs is bad.