If you've paused your automation, contacts who met the entry condition(s) whilst the automation was not live will not enter the campaign once it's restarted, but will instead be skipped.
If you would like to enroll one of the 'skipped' contacts into the automation, you can add their email address via the 'Add Contacts' button on the automation.
Remember to ensure the automation and campaign messages are live before adding a contact in this fashion!