Go to quick export and export these fields:
student_number
First_Name
Last_Name
Grade_Level
Then open in excel and add two column headers, Locker_Number and Locker_Combination . Then assign lockers to students, This can be done in bulk by copy/paste. Once that is done, delete out all columns so you are left only with:
student_number Locker_Number Locker_Combination
Save the file and go into quick import and use the "suggest field map" and it should pick the fields for you automatically. Hit the "Import" button.