@ Sushma.
I think you may be able to do that by connecting the audio OUT of the PCB to the collector pin of an NPN transistor. The Emitter pin connects to the speaker. The other leg of the speaker connects to ground. Then one end of the LDR connects to power. The other end of the LDR goes to the base pin of the transistor. Adjusting the light to the LDR will control how much current goes to the base. This will theoretically control the volume of the audio going to the speaker. I may be way off but that is where I would start.