How do I clean necklaces? Or how do I clean the chain and the pendants for it to be clean?

By using this.

BTW, I couldn’t get your link to work.

Put the chain and pendant into a glass, cover with baking soda,. put the whole thing in the sink. Gradually add vinegar Be careful with the vinegar or it will overflow.

Fill a pot with water and bring it to a rapid boil. Take some aluminum foil and craft a bowl or boat, and put the jewelry in there. Using a pair of tongs, lower the bowl with the jewelry in it into the boiling water, and immediately add 2 or 3 heaping spoonfuls of baking soda. Jiggle the bowl around with the tongs every 20 seconds or so to make sure that all parts of the jewelry come in contact with the foil. After 2 or 3 minutes, remove the foil and the jewelry, and rinse the jewelry off in cold water. Voila!