There are 2 methods for providing multiple attempts for quizzes, depending on your situation.
1. All Students Get Multiple Attempts
If you want to design your quiz to provide multiple attempts for your students, you can do so in the quiz Settings.
To allow multiple attempts:
Go to the Quizzes tab.
Find the quiz you want to adjust, go to the right hand side, click on the 3 dots and select Settings.
In the section at the top called Attempt Settings you can make adjustments to number of attempts, whether you want a waiting period between attempts, and whether the highest score, average score or latest score counts.
2. Give Extra Attempts to Specific Students
Once a quiz has started, if you want to give specific students extra attempts, you can do so in the quiz Moderate page.
To give individual students additional attempts:
Go to the Quizzes tab.
Find the quiz you want to adjust, and go to the right hand side, click on the 3 dots and select Moderate.
Find the relevant student, go to the right hand side, click on the 3 dots, and select Quiz Level Accommodations.
Add the number of additional attempts you want to provide in the Additional Attempts box.