If enabled already, course completion certificates are issued automatically to students upon successfully completing the assessment. This means that when they have scored equal to or more than the passing marks, the system automatically issues a certificate. 

To learn how to enable Course completion certificate, read more here: How to add course completion certificates to my courses 

However, there may be times that a certificate may not have been issued to the student. Additionally, this would also be viewed under the assessment progress status which would not be reflecting any progress for the specific student:

The student may also see the result as failed rather than passed.

In such cases, you can manually complete the workflow wherein the system would rerun the logic and check if the student has cleared the assessment and issue a certificate. 

To do this, login to the dashboard, under courses, click on the course name to access the assessments section. 

Here, click on submissions and access the Attempts section by clicking on the icon shown below. 

In the example shown below, the student is allowed an attempt twice with the passing marks being 26. Here in the first attempt, the student has already scored 28. As such the student has cleared. 

Out of the 2 attempts, since the student has cleared the assessment in Attempt 1, scroll down to the bottom of the page.

Click on Save & Close on the attempt wherein the student has cleared the assessment and the system would rerun the logic. This would result in a certificate being issued to the student automatically. 

Additionally, for that specific student, you would also see that the average assessment progress would also start reflecting as 100%.

So once you have clicked on the Save & Close option, the course completion certificate would have been issued automatically to the student. And the result 

Finally, the student would be able to see the result as passed and will also be able to download the certificate as well.