Quizzes have a moderation feature by which you can grant students additional attempts, and all assignments (including grade bearing quizzes) have 'Assign To' fields where you can define which students can access an assignment. However for Resit purposes, it is normal practice to make a duplicate copy of a quiz/assignment for resitting students to undertake. These duplicate copies can be clearly labelled and attempts can be handles separately from the main cohort. These instructions are for quizzes, and the method used is different depending on the quiz engine used in Canvas.

New Quizzes

The New Quizzes tool uses a special 'LTI' currently in Canvas, luckily the Duplicate feature is very easy to find and use, as identified here: https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-duplicate-a-New-Quizzes-quiz/ta-p/577

Classic Quizzes

There are now several ways to create a duplicate of a Classic Quiz. The easiest way is to use the 'Copy To' option for the quiz, and to copy to the same course. A warning is shown on screen about the effects of copying Content where it overwrites itself and this is understandably worrying where student attempts may be attached to the original quiz, however this function has the effect on quizzes of making a new duplicate copy alongside the original. Instructors following this path may like to use live chat to contact the Canvas 24/7 'Tier 1' support under the Help menu for re-assurance, or if failing that save a backup of the Grades area.

There are other methods such as making a backup of a course and reimporting the quiz from the backup.