When you connect to the VPN, all DNS requests go via the VPN. Otherwise you would have a "DNS leak" if your DNS requests went via your ISP. To resolve DNS leak, you just need to remove the static DNS from your OS, because those are what causes DNS leaks. 

For Windows, you can follow the steps from: https://dnsleaktest.com/how-to-fix-a-dns-leak.html

For Mac OS X, follow these steps:

1) Choose Apple menu > System Preferences > then click Network (if needed, first unlock the padlock on the bottom and enter your admin password).

2) Select the network connection service you want to change DNS for and double-click the connection > then click Advanced. 

3) Click DNS tab, then use the Remove (-) button at the bottom of the DNS Servers list to remove all the DNS servers that are there. 

4) When you’re finished, click OK.

***Linux users should go over our FAQ page here: https://support.blackvpn.com/kb/faq.php?id=74