Is there a way to go in and manually enter the date a user completes the course?

If i understood you right its easy you need to

1.       Login as an administrator

2.       Go into E-Learning ( top main navigation)

3.       E-learning again the drop down

4.       And course

5.       Find the course you want and on the right you have the different features and setting look for the user one ( normally have the number of users and the user icon)

6.       Click on it once it loads on the right hand side you have active form and active until changes these setting

You should be fine now