you can do it two ways
1. Swoop and knock them back (right click) then swoop at them immidiately after and hit them back again This is easier cuz you can control where you go
2. for people slower (ie krillin, trunks) swoop and knock them back, teleport toward them and press the right mouse button to know them back
I prefer the 1st one cuz it's easier
and if you really wanna hit them where it hurts, after you hit them the second time ( you can only knock them back twice no more then 2) you can fire a ki ball or 2 at em, or throw a generic beam or ball at them before they recover.
This is the most common thing you will see in ESF, it's used the most. So get used to it, and try to find ways of not getting hit with it ^.^ and good luck, i suggest fighting humans rather then bots, bots are no where near as good as humans. The more you play with people the better you will get.