You can modify the entries inside an SPF record from inside the cPanel interface. The changeable entries include the following:
Additional MX Servers
Additional IP Address Blocks (IPv4)
Additional IP Address Blocks (IPv6)
Include List (INCLUDE)
Exclude All Other Hosts ("-all" Entry)
1. Log in to the cPanel interface for your domain.
2. Navigate to the following location:
cPanel: Home -> Email -> Email Deliverability
3. Locate the domain to modify, and click "Manage".
4. Locate the SPF record on the page, and click on the 'CUSTOMIZE' pencil icon.