In Live Chess you can find the computers under the players tab and challenge them.
You can also type "/challenge COMPUTER3-HARD 5 0" into the alerts tab chat box. You can replace "COMPUTER3-HARD" to any of the other computers (COMPUTER1-EASY, COMPUTER2-MEDIUM, COMPUTER4-IMPOSSIBLE) and "5 0" with any time control you want, where the 1st number refers to the initial time, and the 2nd number refers to the increment.
Hope that helps! Let me know if you need more assistance :)
i would like to play blitz games against the computer, but don't know how plz help
thx,
seanysean the second