The most important thing to know is that there can only be one SPF record per domain so if you have more than one you need to join them.
Here is what you should do if you are merging 2 SPF records (ie adding PrintJob to Microsoft outlooks SFP)
Change the Host: as outlined in red and add another include:spf also marked in red.
TXT Value: v=spf1 include:spf.protection.outlook.com include:spf-s1.printjob.com ~all
Information about what SPF data needs to be added can be found when you click Authenticate Email. These instructions vary depending on where you are based in the world but overall they look something like this.
SPF records take time to propagate so be a little patient.
If Host: is giving you trouble you can replace your domain with @ and it should work.