There is a tab where you can enter values going back in time for a single statistic. This is indicated by 
and the tab is called Values by Statistic.
Next select the statistic from the dropdown list as shown by 
below.
Enter stat values and any note in the grid indicated by 
below.
The refresh button 
updates the values in the grid as these may have been edited by another user.
Use the save button 
to save the values you've entered or changed to the database.
The undo button 
undoes any values you have entered or changed but not saved.