Hi Phung Thi Thu Ha
Here you can register https://academy.mendix.com/link/certifications/22/intermediate
Yet, as you can see: there are no slots available at this moment. You can either wait untill new slots open, talk to your Mendix contact at your firm or you can contact Mendix Support for this.
I hope this helps!
You can register for Intermediate certification from the Mendix academy.