Unfortunately, it is not possible to reverse the results of any games that have ended — they've already been recorded in the past
game histories and factored into the ratings and stats for both you and your opponents (and already affected the ratings of any players they've played against since then). Please simply continue to play and win more games and you will be able to restore the lost rating points in no time.
It is not as bad as it sounds however, as the rating system works in such a way that it automatically corrects any sudden dips in one's rating over time, if it doesn't correspond to reduced playing strength. The rating formula is based on statistical analysis and makes any previously completed games have progressively less and less influence on your current rating as you finish more games. It happens because the rating points awarded at the end of each game are calculated based on the difference in the ratings of the 2 participating players. Which means if your rating drops suddenly, you will be gaining relatively more points after each win after that (and losing relatively less points after each loss), which will even out the previous "dip" in your rating as you finish more games.
Also, please refer to question #8
for more information on how to request game reinstatement. But please note that it will not erase the results of the timed-out game(s).