To add Aliases domain you must first check nameserve same as your current domain nameserver linked with your hosting. Go to cPanel from following link: 
https://www.yourdomainhere.com:2083 
- enter your username and password
- Go to Domains section
- Then Aliases
- In first field insert your new domain.
- Select add domain. 
Great!, Now you can open your website with new/old domains.