- Log in to cPanel.
- Go to > Email > Email Deliverability.
- Locate the domain to modify, and click Manage.
- Locate the SPF record on the page, and select the 'CUSTOMISE' pencil icon for the record.
- Review the settings and modify as required following the information on screen.
Please see detailed instructions from cPanel here
NB the SPF record can also be edited via Domains > Zone editor, but the above method provides an interface specifically designed for SPF.