Select the students you want to update the emails of from the Start Page by choosing a filter, then using the Group Functions Dropdown and choosing Quick Export
It should bring you to Start > System Administrator > Page and Data Management > Quick Export
For the fields, you want Student_number and Student_Web_ID
Make sure the delimiter is set to Tab and Column titles on 1st row is checked
Click next
From there, you'll get a text file with the information, open it up in Excel. It should look something like this
Delete out rows with no username
In Column C, put '@student.hancock.k12.mi.us (or whatever the ending email is)
The ' is key in making excel accept the email ending and this will not work without it
In Column D Insert > function > concatenate (Format is CONCATENATE(A2, B2)
Drag the formula down for all columns
Remove columns B and C, which should make D the new B
Create a header called Student E-Mail for Column B
Save the file
Go back into Page and Data Management, then Data Import Manager
For Source, pick the export file you edited, pick Student Email to import it into, and then click next
Make sure the PowerSchool Fields make sense, then click Next
Click Update existing record
Wait while it processes. It may not show any "new" records, so to verify, return to the start page, select a student, and go to their email from the information tab. It should show up there.