How to reply this mail from potential PhD professor?
I doubt that any reply is expected. It seems to be a general response and may not have actually come from the professor, but from his/her office, instead. 

I wouldn't expect much of any response until the deadline for application has passed. I suspect that viable candidates will then get further information about what else might be needed. 

But if you haven't completed your application by submitting required materials, it would probably be good to do that soon.