Step 1: Disassembling
There are 5 screw 2 for holding body 3 for the speaker part, since you are not going to use it again, you can just rip off the sponge and you'll reach to 3 screws.
Step 2: Soldering
Before soldering I've used crocodile cables to find out which cable belongs to which audio channel.
For audio cable, you can just cut a audio extender cable.
Soldering wasn't easy for an amateur like me. First, burn thin cables carefully with a lighter so it will remove the protector part over the headphone cables then you are ready to solder.
Step 3: Make It Together!
Well the last part is only depends on you. I just simply glued via hot slicone left cover to right cover to make it looks nice. Also for avoiding and troubles and for making it durable, cables also sliconed. There was enough space to put battery inside the shell but sometimes battery can be heated up, so I think it is better to leaving it outside!
Voila! Your new bluetooth audio receiver ready to work with all kind of speakers!