In the Campaigns section, you can cancel a scheduled or draft campaign.

You must click on the three dots on the right and select 'Delete campaign':

The campaign will update its status to Canceled if it was scheduled, or it will disappear if it was a draft.

If you select Edit, you will also have the option to cancel the submission.

Remember: you can edit the campaign or modify the send time up to 10 minutes before the scheduled time. Once that limit is exceeded, the campaign will be sent.