Hi Samuel,
You can log in to SAS Management Console, select SAS Folder tab and double click on the report in the metadata location. You can see the Responsibilities list in the bottom of the pop up windows. You can add use as a owner.
To reschedule your ex-colleague's reports, you should be able to do it if you belong to "Visual Analytics: Administration" role. Or you can try to reschedule it in SAS Management Console -> Schedule Manager.
Regards,
Ryan Kwok