You can use more dish soap to make more slime, but you'll need to add more cornstarch as well.  Consider using some colored or scented dish soap. For a more traditional slime, consider green dish soap. You can also use shampoo instead of dish soap. The thicker the shampoo, the better!

TL;DR in Vietnamese:
Lấy 1,5 thìa canh nước rửa bát cho vào bát.