I have a plan of what I want to do but no idea how to do it! If anyone can tell me if its possible and how I would go about doing it would be really helpfull.

I have a form called "Mark_Class_Roll" which has a subform in it called "Student_List". 

To mark a roll, I enter:

the date of class

the head coach of the class

the class name

Then the subform autopoulates with the names of the students in the list. 

All of this is shown in the image below:

When the roll is marked it creates a record for each subform row which is saved in a report. Like the image below:

What I want to do is:

If an athlete contacts us to tell us they will be away, I would like to enter that information by inputting the future date that they will be absent and then completing the subform and saving the records.

When I go to mark the roll on the day and I input all of the information into the main form I would like it to pull any subform records already created for that information (ie that date and that class) and input that into the subform to update the rest and then save again.