Go to https://mxtoolbox.com/spf.aspx, enter your domain name (without www) and click on the orange "SPF Record Lookup" button.

The following page is shown. (As example we use the records of our domain)

The green shaded area shows the current structure of your domain's SPF records. This will always differ from the above image. But you can see in our example that the required SPF record


 is included. That is what you or your domain host has to add to the DNS zone of your domain.

Does your SPF check result also show this line? Perfect, than you have successfully added the record!