There are a few ways to mark your students as absent or enter in another reason as to why they did not receive service.
Once you have filled out the Quick Select and are taken to the Service Tracking Grid, scroll to the right until you find the column labeled "Missed Service"
Double-clicking the cell will give you options as to why a student did not receive service, this list of Missed Service Options can be customized by an Administrator (Check out our Help Center Article Edit Missed Service Options (Administrator Only))
If multiple student missed their service, the Service Tracking Grid will allow you to click and drag as well as copy/paste to speed this process up. Check out our article Using the Service Tracking Grid to see how.
If all students missed service you can use the "Missed Service" option on the quick select.
Note: Selecting the Missed Service Option on the Quick Select will apply to ALL selected students.