How to make silky smooth chocolate like galaxy bar or dairy milk bar from chocolate compound?
Very short answer: you can't.
Making smooth chocolate bars is an industrial process, not replicable in the home, at least not with reasonable amounts of effort and money. You need specialized know-how, equipment, and access to the proper raw materials.
Also, compound chocolate is not suited for making chocolate bars. It is a different end product, meant to be used as a cheaper and easier-to-melt alternative to proper chocolate bars, it is not a raw material for chocolate bars.