Not bad, if the doctoral thesis is only submitted to the school system without filing, it can still be resubmitted and covered. But the tutor must find your problems and give suggestions for improvement, and let you resubmit them, or talk directly in private to let you revise your paper, correct those mistakes and resubmit them, that is, you can still revise them.

The submission of doctoral dissertations, like the submission of master's dissertations and undergraduate dissertations, can generally be submitted many times, because it is impossible to pass them at one time, and there may be problems many times, and every time the tutor contacts you to ask you to revise them, then revise them to a final paper that meets a standard, and finally submit them.

If it has been submitted in the end and has been put on record, it is impossible to revise it, that is, it cannot be submitted repeatedly, nor can it cover the previous paper and submit a new one.

So the doctoral thesis depends on whether it is submitted for the last time. If it is the last submission, it cannot be modified. If it is not the last submission, it can be modified.