You can withdraw a role if you no longer require a supply teacher, up until the point that you've extended a formal offer. You are also able to withdraw a role if a formal offer is rejected or lapses. To withdraw a role, go into the live role and click the button on the right that says 'Withdraw'. A history of withdrawn roles is viewable from 'Roles -> All roles' menu
If you need to withdraw a role after it has been formally offered please contact Airsupply.