EMDR therapy does not try to erase or suppress unpleasant memories; rather, it combines "bilateral stimulation" such as eye movements, tapping, or buzzers, with activating the memory of a past event (or events) in order to help the brain process information that is stored in the brain and body from stressful or traumatic events stored in a different way.
The hope is that after EMDR, when triggers or reminders of the bad thing from the past arise, your physical and emotional reaction will not be as overwhelming and you will be better equipped to handle related challenges as you go into the future.