Starting noticing vvv slightly darker skin as compared to the rest of my face around my lips

Im 26, fair and cool tones
I only use cerave hydrating cleanser and cetaphil lotion on my face.

What can i use to stop this from progressing?

I have noticed yellowish skin on the sides of my lips and a bit darkee on my upperlips.

What one product should I start?

Azelaic acid? Nicinamide? Im such a noob when it comes to skincare 😭😭