Resetting problem attempts for Open edX students
Every now and then you might have to allow a student to retake an exam, or perhaps throw out an entire question of some assignment because students didn't understand it. Whatever the case may be, there's a good chance you're going to need to know how to reset student attempts on a problem. Here's how it's done:
Let's say we have a student who terribly misunderstood this particular problem and incorrectly used all of the submission attempts he was given.
Thankfully, being the gracious instructor you are, you decide to allow this student to try again. In order to do this, start from your Staff LMS, and navigate to the problem in question. 
Click on "Staff Debug Info" 
This window provides a lot of information. All we need to worry about, though, is the top section, under the heading "Actions" 
To reset a student's attempts, simply type that student's username in the given field and click "Reset Student Attempts" 
You should get a success message, and now the student will be able to answer once again!

That's all there is to it!
ALTERNATIVELY...
There is another, slightly more complicated way to reset student attempts on a problem. However, it does give you a few more options, such as reseting attempts for the entire class, which can be useful. Here's how that goes: