I've been trying to bulk for the past 2 months and yeah I did grew lots of muscle mass and weight. Currently stands
at 18 years old with 173cm 68-70KG with 21% bodyfat.

My abs cant really see clearly(compare to before I bulk) during the half way bulk but I gained massive size.

But luckily I don't have tummy considering my bodyfat is quite high lol .

Right now I have decided to cut since I have already gained the size that I want.

But the problem is I don't really know the method to cut.

I watch some youtube about their advice on NOT cutting calories in 1 go because u might lose muscle mass as well.

Should I be doing LOTS of cardio while lifting heavier weights and cutting calories bit by bit?

Advise needed. Thanks

Go 10% below TDEE first.

20% below TDEE at max or u risk major muscle loss.

Make some reverse dieting as well. Don't eat from surplus suddenly to deficit.

Let say your bulking calorie now is 3000. Your maintenance is 2700cal. You want to cut at around 10%=2400.
Every week, decrease your calorie intake by 100 starting from 3000, 2900, 2800... until you reach 2400. This is to ensure your metabolism doesn't drop significantly and you can eat much food while cutting. Correct me if I'm wrong.

Yes this is right. Advisable drop slowly to maintenance then deficit so you don't get that starve effect.