by letting them know do you mean like just telling a random girl on the street ?
or big companies that you maybe see a female colleague you interested but you have never talked or worked ith her before?
or need to be at least friends and have their number ?
because I see most is they dont meet any new female friends. so how to even tell or proceed. if they try to meet new female friends in public setting some may think is harassment.
if you're talking about picking up random women on the street/ mrt/ shopping mall, tbh SG doesn't really have a pickup culture and MOST local women are quite reserved. But this kind the face card must be damn up there - no need Andy Lau level, but at least above average + look like you work out. And even then you should expect to be rejected more often than not unless your face is really korean oppa.
what works is always dont be a creep. meaning:
i) go get your health in order, dont look like a bbfa (yes, looks still matter for a vast majority of people)
ii) start small, nod and smile if you see someone cute in the office. if they reciprocate start to slowly scale up to a convo "ive seen you around recently, are you new?", "how was your weekend" and try to find common topics. extra note that you should try to do this to everyone, not just women in the office. because talking to more people about random things and making more friends helps you to loosen up more in the office, and your image will change from the creep that always talks to young fresh female hires to the friendly guy in office.
aside from this, find new hobbies and join meetup groups like run clubs. go there with the intent to find like-minded people and enjoy your hobby. Note that you must NEVER EVER join with the sole intent to date, because everyone can smell desperation from a mile away. if you find someone cute there, good for you. if not, you've just made 15 more friends that know you're a decent guy that's single and available and you'll get more people trying to set you up.
finally, dating apps lol.