Most people must apply online to extend their study permit from within Canada. You should submit an application to extend your study permit before your current permit expires.
If your study permit has already expired
You need to restore your status as a student, as well as extend your study permit. You must apply to restore your status within 90 days of losing it. If you don’t, you must leave Canada.
You can’t continue your studies until we restore your status as a student in Canada and extend your study permit.