All firms, bodies and self-employed persons in operation must comply with the safe management requirements here and sector-specific requirements here.
The list of services that are currently allowed to resume operations and their corresponding Singapore Standard Industrial Classification (SSIC) codes, can be found here.
Please note that your SSIC code should correspond with the Primary Business Activity in your business registration records with the Accounting and Corporate Regulatory Authority (ACRA). You should ensure that your business activity is in line with your selected SSIC code.
If you do not know your SSIC code, you can login to BizFile+ using your Singpass.