I made an edit that was submitted for review and quickly noticed I made a mistake. How can I unsubmit it?
You can edit your suggested edit by clicking "Edit" on the post again. Any changes you make will become part of your original suggested edit. I think this is what you want.
Unfortunately, there isn't a way to completely retract suggested edits, so if you want to do that, you have to contact another user with permissions to edit posts. Usually, they will perform some other concurrent edit, so that your suggestion gets automatically rejected as an edit conflict and doesn't count negatively towards you.