How to have tax relief in Singapore. I heard can use cpf but I'm not sure how

You can refer to the 2nd section on lower taxes in this article on why you should top up your cpf! i think you can get tax relief when you do cash top-ups to your own or your parents’ cpf accounts

Contribute to your MA via VCMA (voluntary contribution), or contribute to SRS. However do note that both have a cap for tax exemptions; MA being $8000 and SRS being $15,300 annually.