Some cheap single freewheels aren't intended to be removed and don't have notches or splines for a remover tool. The only way to remove them is to disassemble the mechanism. A pin tool will unscrew -- probably reverse thread -- the cone, causing the cog to separate from the freewheel body, and allow a pipe wrench or similar nasty tool to grasp the freewheel body and unthread it from the hub. This is generally a destructive process. But are you certain you need to remove the freewheel in the first place? If you can remove the locknut and cone from the fixed cog side, you may be able to slide the whole axle out of the hub leaving the freewheel in place. Check this before destructively removing the freewheel.