If you have failed syncs originating from Magento you can retry the sync from within the DSYNC Magento plugin.
Before you do this it is recommended to troubleshoot why the syncs failed before retrying.
From within the Magento Admin Panel select DSYNC then select Process Notifications.
A list of syncs will be displayed,
All Successful syncs will be displayed with a status of Complete while failed syncs will be displayed with Error.
On the right side of each error you will see a retry option that will retry the sync.
If the status is still marked as Error you can select the error to get further information about the failed sync, you will also need to login to the DSYNC dashboard and view the logs to help determine what the issue is.