To edit an employee's timecard, navigate to Financial ➡️ Timecard Management
Enter a date range, select an employee, and pull up previous time cards.
Inactive employees are listed at the bottom of the list, in case you need to pull timecard information for someone no longer employed at your company.
To edit a timecard entry, hover over an entry and click on the pencil icon on the right side of the table. You can also delete an entire entry. 
To add a missed day:
Create an entry from the employee's home page by clicking on the "edit entry" button. Choose the day and enter the time then click save.