Not the biggest tutorial so I'll cut right to the chase.

The wrinkles and creases need to be preferable made onto a high-poly topology obviously so that they're different from the base model. It doesn't matter really if your base model already has pores added, you only need to add extra detail onto the duplicate.

You need both your final unchanged high poly model and the duplicate, but with the changes you added (such as wrinkles or creases in this case)

Basically, just load up the base model in Substance Painter, then in the Bake -tab, choose the model with the creases as the high poly cage, choose normal map to bake (or any other map, I suppose this method works with all of the bake options), then choose the usual bake settings that work best for you and notice that with the result, only the wrinkles appear on the normal map. Everything else appears as 128 128 255 blue.