Hi @NeridaG 

There are instructions for submitting an assignment on behalf of a student at https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-submit-an-assignment-on-behalf-of-a-stu... 

Please note that the "Submit on behalf of..." is a feature that must be specifically enabled in the school's Canvas instance.  If you do not see the option described in the article, you will want to contact Canvas Support at your school.