Entering a job that was completed in the past is the same process as scheduling out a job for the future. The only difference is you'll choose a past date.
To do this, go to the schedule screen as usual. From here you can use the arrows or click on the dates to go to the date that the job was completed on.
If you select the dates provided, a drop down calendar will appear where you can choose which dates you would like to see on the calendar.
When the correct dates are showing on the scheduling calendar, just click on that date at the correct time to move the job.