Entering DNS files

I have a website set up to send subscribers e-mail notices when I do a post. Some subscribers don't get the notice. I was advised to subscribe to a service, WPMail, for help in resolving this problem. WPMail connected me with Sendinblue, which created DNS files to add to the domain zone in my web host, A Small Orange, but I am unable to see how to do that. I need somebody to review my correspondence with Sendinblue and take over for me in following their instructions. I'm not a technical person and I don't even know if I'm explaining this right, but I have a feeling that someone who understands this stuff could get int done very quickly.