METHOD 1
Just DDOS the waf's IP.
[HOW TO GET IP]
Add a website to it then it will show you a CNAME domain,ping it and you get your IP.
METHOD 2
Setup a real website on it and use cc attack to drain it's bandwidth.
Firstly, setup your website.
Then put some ** on it and share it to foreign SNS.
Or you can setup another machine to cc the waf.
[CAUTION]
Be aware of closing all the anti-attack options and cc it.