Can't find the datasheet of cheap Bluetooth audio reciever
If you already searched for the chip and didn't find with Google, chances are that you will never find this datasheet...
If I were in your situation, I would try to use this module just as every other
cheap Bluetooth module. If you succeed, good. But, if don't.. well, with no datasheet, you have nothing to be lost here; the only thing to do would be order another cheap bluetooth module.
If you send a photo of the back of the PCB, we could give more hints. This is my &quot;educated guess&quot;:

AUDIO
1 Left (or right) output +
2 Common (audio ground)
3 Right (or left) output +

POWER
4 +Vcc
5 GND

If left and right are interchanged, well, who cares? But you can change they, if needed.
Look that pad 5 is connected to a great area of PCB, that's why I guess that pad 5 is GND.
There is a white retangle around pads 4 and 5, so that it seems that they're the power connection.
Probably pads 2 and 5 are connected one to another? (check the other side of the board)
For probe this board: connect pad 4 to 3.3V and pad 5 to GND, and search with a cell phone for a bluetooth device.  If don't suceed, try at 5V.