Did you check the error due to which it failed ? Fix that issue that caused the job to fail and re-run the job (you can right click and "Start Job")...and if the issue is fixed, then it will run again at it's scheduled time. If it failed because of security issues, then you would need to look into the account under which the SQL Server Agent is running and what exactly that job is trying to do (like using xp_cmdshell etc.).