1. Make sure you have addon DNS management tool with us.
2. Login to client area.
3. From the top menu bar, select Domain, My Domains, click Manage Domain. Choose Management Tools and select Manage DNS from drop down menu.
4. Choose Nameserver from Menu Tab, add below nameserver:
5. Choose Management Tools and select Manage DNS from drop down menu.
6. Refer to below image, add the A and CNAME. Please note that yourstorename.myshopify.com is your myshopify.com subdomain.
5. Click Save Changes to save the setting.