Shall you register the domain with third party provider and purchase a hosting account with us, you may need to login to your domain provider's control panel/ account portal to change the domain nameserver to us.

Depending on the format of the third party provider , you may change the nameserver via their client area, billing portal or client area. Shall you are facing any issue may contact their respective support to assist with the nameserver pointing. 

Next for the domain nameserver details, you may obtain them from your Welcome Email on Server Information section.