Hi Feyza,
The Moodle quiz has the option delete an attempt and the user should be able to attempt the quiz again. If you have time limits then you can also tell Moodle how to handle the attempt after the time runs out, so you can tell Moodle to submit automatically and the user will at least get some kind of grade even if they had internet issues. See below links to both options.
Option 1 with quiz attempt deletion: https://docs.moodle.org/310/en/Quiz_reports
Option 2 with Quiz options: https://docs.moodle.org/310/en/Quiz_settings#Timing
The Moodle quiz has the option delete an attempt and the user should be able to attempt the quiz again. If you have time limits then you can also tell Moodle how to handle the attempt after the time runs out, so you can tell Moodle to submit automatically and the user will at least get some kind of grade even if they had internet issues. See below links to both options.
Option 1 with quiz attempt deletion: https://docs.moodle.org/310/en/Quiz_reports
Option 2 with Quiz options: https://docs.moodle.org/310/en/Quiz_settings#Timing