Use a mild dishwater soap
Apply Food Grade Mineral Oil (top, bottom and all sides).
Once a day for a week – Once a week for a month – Once a month forever.
Mineral Oil can be found in many stores in the digestive lubricant section. Brand doesn’t matter. Food grade mineral oil is… food grade mineral oil. USP at the end means United States Pharmacopeia. That means the production meets their strict requirements. You can buy “cutting board oil”, but you are just paying for branding and marketing!
If you want a protective coating, you can get food grade mineral oil with carnauba wax mixed in, but I wouldn’t do that until you get deep penetration of the oil first, after 3 months.
A good practice – after you clean with dish soap, let dry, next day apply mineral oil.
Lender Gifts Cutting Boards Last for Decades with Proper Care.