All you can do is paint. Porcelain is a type of ceramic and is made by firing in a kiln in a factory. Epoxy paint is your only choice that will hold up for awhile. Kits for that are sold at home depot and step by step instructions are in the kit. You should get several years of use out of it as long as you don't chip or scratch it, then it will peel.
Hi Sheila, if it's white, this may work for you. I was amazed at what Cerama Bryte did to mine. It was marred and had rust stains. It had a few pits but once cleaned you can't even notice...you can peek if you like: https://www.exquisitelyunremarkable.com/2018/06/best-way-to-clean-a-white-porcelain-sink.html
Here is a helpful article https://www.hunker.com/12318364/how-to-resurface-a-porcelain-sink
Here is a good tutorial: https://www.hunker.com/12318364/how-to-resurface-a-porcelain-sink
I've used this paint on a bathtub and it worked well: https://amzn.to/2FS5dpB