[Routine Help] Which face serum should I use?

Hi, my skin is pretty dull, I don't have acne. I'm currently using a Minimalist moisturizer, Plum 3% niacinamide a rice water toner as my skin care routine nightly. It does not look like it had any effects on me, maybe because I don't use it regularly.

I'm thinking about using a face serum to tackle the dullness but don't know what kind or brand, presumably looking for korean ones. What serums worked for you? Please let me know.

Also, i have dark undereyes. Any suggestions for that are appreciated too ❤️