A quick search found this quite detailed routine, I’d suggest start simply and work your way up - this will help identify what’s working and if anything gives you any issues:
Improving dull skin takes time and patience, but this routine should help the skin shed it’s hyperpigmented cells revealing a bright, clear, uniform skin tone.
Glycolic Acid 7% Toning Solution or Brightening Toner
Alpha Arbutin 2% + HA and/or Niacinamide 10% + Zinc PCA 1%
Ascorbyl Glucoside Solution 12%
Azelaic Acid Suspension 10% (as a moisturizer and/or Natural Moisturizing Factors + HA if your skin is dry)
Resveratrol 3% + Ferulic Acid 3%
Vitamin C Suspension 30% in Silicone
Granactive Retinoid 5% in Squalane or Retinol 1% in Squalane (on alternate night to the ATS 20% and R 3%+FA 3%).
100% Organic Cold-Pressed Rosehip Seed Oil.
Extras: AHA 30% + BHA 2% Peeling Solution or Lactic Acid 10% + HA as a weekly treatment.
I personally prefer this Vit C - as it just feels more cosmetically sophisticated I believe is the term…