Keep it simple young man.
Use a zinc oxide cream topically dawn to dusk that will act as an astringent plus physical ☀️ protection and this will help prevent the darkening.
Apply a collagen remodeling cream topically evenings eg Cicabio (Bioderma product)
...both creams mentioned should be able to be procured OTC.
Next Steps
Keep Pics before and at weekly intervals and present pics and consult Online in about 2 weeks.
Health Tips
Kojic acid creams can be added to the mix after a week to help lighten the area if deemed necessary after viewing the documentation of pics objectively.