How to get value of field in current record

How to get value of field in current record

Hi,
I have a table called 'Classes'
In that table, I have a field called "Class1" - it is a drop down field.

On the action "On user action", I want to save the value that is in the field if a user removes that value. So, if the value in Class1 == null, I want to know what it was before it was removed and save that value in a variable.

This gets me the value that is in the field before it was deleted.
 ctemp1  =  Classes  [ID == input.Class1];

How do I save that value though after the field value is deleted?
I need to use that value to remove a record from another table (Call it "Class List")

if a user puts a value in Class1, I write it to "Class List".
If a user removes a value from Class1, I need to remove it from "Class list".  <-- this is where i am having trouble.
Thanks!
Mike