Hello there, @HyeeunJang ...
It is possible that your school's local Canvas administrator(s) have hidden the button from instructors that allows for course resets. Check out the blue box at the top of this Guide: How do I reset course content? - Instructure Community (canvaslms.com). If you don't have this button, you're going to need to speak with someone at your school who has administrator rights to your school's Canvas account. This person should be able to help you reset your course for you.
Good luck. Take care, stay safe, and be well.
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