How to ask for a pay raise?

I (28F) would like to ask for a pay raise but not sure how to approach this topic as I’ve only joined the work force 3 years ago (1.5 years in a startup and now 1.5 years in current company) - long story short, never requested for a pay raise before.

For context, my base pay is SGD7k monthly inclusive of own contribution of CPF (non-inclusive of employer contribution). Adding my quarterly bonuses, I make about 108K per annum. ~ Works out to 9k monthly.

Though it is a decent pay, I do think that I deserve higher base pay compensation. For several reasons - Since I joined, have brought in revenue that covers my base pay & more (hence the quarterly bonuses) - Managed to secure deals from clients who previously do not deal with company at all - Found out that colleague who is severely underperforming and has in fact incurred losses for company is earning the same base pay as I am

Not sure how to approach this with my boss at all (imposter syndrome perhaps) and since I am still relatively new and in a junior role, not sure if I’m pushing my limits here. Any advice would be much much appreciated, especially if you have any in retrospect of how you’d approach this in the start of your career

Thanks lots in advance! x