Kim, who is dating rapper Kanye West, revealed at London's Aqua restaurant: "I look back at things from really recently and I'm like, 'Oh my God, why did I wear that, what was I thinking?'
"But it's fun. You see what you like and what you don't and experiment."
And Kim, who wore a black sequinned mini-dress for the launch, said her famous boyfriend has been supportive of her latest business venture.
Kim and Kourtney worked on the range with sister Khloe, who was unable to attend because of filming commitments on the US version of The X Factor, which she co-presents.
Mum-of-two Kourtney praised British women's "individual style".
She said: "It's not like matchy-matchy, everyone in the same thing, it's very different."
Kim added: "It's amazing. I think they have such great style, very effortless and chic, that's why we're really excited to launch in the UK."