To remove yellow stains from the sink surface, you can try the following methods:

1. Lemon and Vinegar Mixture: Mix the juice of a few slices of lemon and some vinegar. Apply this mixture to the areas with yellow spots. Leave it for a while and then rinse with warm water.

2. Sodium Bicarbonate (Baking Soda): Apply sodium bicarbonate mixed with a little water to the sink surface. Then scrub with a sponge or brush. The natural abrasiveness of sodium bicarbonate can help remove stains.

3. Salt and Lemon: Create a mixture of lemon juice and salt. Apply this mixture to the stained areas and rinse after waiting for a while.

4. Oxygen Water: Spray oxygen water on the sink surface and wait for a while. Then scrub with a sponge or brush. Oxygen water can help remove stains and dirt.

5. Homemade Cleaner: You can create a natural cleaner by mixing liquid soap, water, and a few drops of white vinegar. Apply this mixture to the sink surface, wait for a while, and rinse.

6. Household Sink Cleaners: You can use household sink cleaners that you can find in the markets. However, be careful when using chemical cleaners and use them according to the instructions.

After trying these methods to remove stains, rinse the sink with plenty of water and clean it. You can also prevent stains from reoccurring by cleaning the sink regularly.