Jon decided to do it later. He figured that maybe he needed more time to think about which of her memories to change. As far as he knew, these changes were permanent. He didn't want to make rash changes that could last forever.
So, Jon and Karyn ended up walking to school, where there were many targets to be found.
And when they finally got there, Jon had spotted several potential targets for his new device. "Now, who's first?" he pondered, with a smile.