Set up authenticated domains on third party platform

I am in need of assistance to set up authenticated domains on a third party platform. Our commercial B2B email marketing platform requires us to set up multiple authenticated domains for our business. Our company already has its domain registered, however, we need assistance to configure and set up authenticated domains for our new email marketing domains. I need support in setting up at least 3 or more authenticated domains as I am not knowledgeable in the setup process. Your expertise is necessary to make sure our email marketing domains are securely and correctly set up.