I bought a sterling silver product and after a certain period some of the silver has oxidized/blackened. What can I do?

To clean and maintain jewelry items from oxidized/blackened you need to
Keep your sterling silver Judaica products and jewelry looking their best with proper care. After use, clean them with silver cleaning materials such as ”Silvo Metal Polish” and make sure to dry them promptly. Store them in a cool, dry place to prevent tarnishing. Remember to keep silver jewelry away from damp areas and avoid wearing it in the shower or swimming pool to maintain its shine.