The first thing you need to do to manually add a DNS-record in your control panel is to log in to cPanel. Depending on what DNS-record you want to add you need to do the following:
If you are going to create and edit A or CNAME-items you go to the Simple DNS Zone Editor, which you can find under the Domains section in cPanel.
If you are going to create and edit MX-records you press on the MX-mail icon, which is under the Mail section of cPanel.
If you are going to create and edit SPF-items you do that through the Authentication icon in the Mail section of cPanel.