I could not find the wheel. I'll give it another shot.

 

Look inside the drum with a light, It's kinda thin, it should turn easy one way and should catch on the lock the other way, If you cant find it take the tire off and the drum back off and look from the outside so you can see what you need to do, You can tighten it up some from the outside with the drum off, then put drum back on and feel how tight it is. When you tighten it up don't go so much it wont turn by hand. You should just start to feel the shoes rubbing,