Quick answer
This is possible using a number of different methods.

Full answer
This helpful guide explains how to manually regrade quizzes, or add extra marks to all quiz attempts at once (https://moodleuserguides.org/guides/manually-regrade-quizzes/).
You can also automatically regrade quiz questions (https://moodleuserguides.org/guides/automatically-regrade-quizzes/), if you need to change quiz or question weightings.