Are you sure that you didn’t do it correctly already? those 6 random characters are a kind of salt which is unique to each one-click install. If you did a one-click install, it should have set up the DB for you with a different salt, so restoring from your backup should not conflict with the tables already in there.
Anyway, what you need to is get rid of your database, start a new one, load it up with your backup, then configure WP to use it. That means you’ll need to edit the wp-config.php file. I haven’t done it in a while, bit I think there’s a place where you specify the table prefix which, in your case, will be ‘wp_q2icxk_’