On the older blue ones... There is a slit in the cover with a little paddle under the opening... If you just press your finger in there hard enough you can depress it far enough to get the switch to come on... I have also used a zipper "handle" to push it in before i knew my finger fit...
Pop the white tab out and reverse the tension spring that is attached to the white pice of plastic. The fan will now turn on and off by just using the switch and no refill.
I have the camo color one but the white tabs on the inside should be the same.
I am trying to work out how to reverse the fan so it will make it a true air mover.