It just means that you're going to go take a shower, but 靚 here is not to say that you're going to make yourself look good after, but you're using 靚 as an adjective to describe how the shower is going to be like-a good shower. 返 (more of a verb normally) here can also be or should be 番 (which is an adverb), but it doesn't mean in this situation "again" or "to go back to". It can also be excluded and still function fine, but it adds some more feeling somehow and sounds a bit more natural and Cantonese-like that way.
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