Seeking your Help.

With little background, it’s tough to understand what’s your current status in Singapore.

If you are a foreigner and not working/staying in Singapore then first reach out ROM with your details if they will grant you and your partner to do annulment here, then based on that confirmation you both can visit here. Inform ICA at the time of applying visa. Good luck

Thank you very much Sir for your prompt reply. Actually I am foreigner and my Girlfriend Singaporean.

In that case, she can sponsor you to visit here. Before that, reach out ROM to understand the requirements and the documents you need to carry including a confirmation letter from your local country office that you are not a married person or if had married earlier but completed filing divorce process. Good luck

You are allowed to marry (ROM) while here on an SVP (tourist visa) and there is no need to inform ICA about this.
However, this does not give you the right to reside in Singapore - you must leave before the SVP expires.
If you want to move to Singapore after marriage, you must apply for an LTVP at ICA or any Singapore embassy.