After Ken and Davis DNA digivolved, the other didn't think that they can do it but think again.
In the episode, Opposites Attract, they were walking through a forest when Gatomon remembered this spot like it was yesterday. It was where she lost her tail ring! So they decided to look for it, so they can fight off BlackWarGreymon. Davis was the one who suggested this idea, and he actually won points with Kari but think again. Kari went with Yolei and Davis was left hanging.
As they started searching, but no luck, then Kari heard in the distance, someone in trouble. It was Ken, so Kari was too the rescue, Gatomon hates when she does this. They started running after her, so in a minute they found him with Wormmon.
To the point:
A new monster was created from Control Spires, Blossomon! When Hawkmon and Wormmon digivolved into champion, Gatomon was about to armor digivolve when Kari was scared. So Yolei slapped her to cool her down and it worked. Then Kari got it together and a bright pink light started to shine. The others noticed that Kari is the darkness worst enemy and sure enough, something wonderfull started to happen. Kari's and Yolei's digimon DNA digivolved into... SILPHYMON!
That's how they DNA digivolved.