Step 1. Log in to the WHM
Step 2. Type list account in search bar and then click on List Accounts.
Step 3. Now click on "+" button which is next left to the your domain name. It will display all options related to this hosting account and now look for Modify Account option.
Step 4. Click on dkim and spf options respectively to enable it.SPF/DKIM used for email authenication.