Hi,
You allowed him to continue with you for one more month to complete your project after his resignation?
After resigning and completing the notice period as per general employment conditions, the employee deserves to move on, and the employer needs to release him with his dues/F&F respectively.
Since he has stayed for one more month with you just to complete your project work, ideally, he should have left on his own accord as he has already taken action by resigning. However, since he has not done so, you need to ask him whether he wishes to continue with you or leave. If he wants to go, you need to release him immediately; otherwise, he can be reappointed.
In simple terms, you cannot remove him from the job as he is already free from employment conditions and is now an ex-employee. You need to inform him that he can stop coming as the work for which he was requested to stay longer has been completed, along with his F&F statement and dues. You can also ask him to come later for his F&F, if required.