Zhang may have a better solution, but in the meantime; you can create a new user w/ password in mysql and replace the "user=" and "passwd=" lines to the new ones. Alternately, if you kept the tips file you may be able to glean the information from it. mine was originally written to /tmp/iRedMail-0.8.4/iRedMail.tips. locate yours using find / -iname iRedMail.tips.
In the future I would make a backup of any config files before opening them with an editor.
Good luck