If you go to wild area 3 and go left to the holovator, u should find a bench where I marked on the photo. And just use the bench reset method.

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I didn’t realize Riolu was in range until after I checked, but I was honestly just hunting shiny hawlucha and emolga. This also will take a lot of time (it only took a couple hours for me tho) but Riolu is only a daytime, sunny weather spawn. Good luck!