Issues with Moosend / help with Google Postmaster Tool

We are having issues with the DNS Record in Moosend.
The DNS has been updated and within Moosend everything is showing as verified however the open rate of the newsletter we just sent out had dropped by 20% and a lot of the emails have gone to junk folders.

The Moosend helpdesk suggested as an additional check we should implement Google Postmaster Tool to provide us with a TXT record to the DNS of our domain to provide proof of ownership/access.

Once done we need to then take a screenshot of the last 120 days of the Domain Reputation report.

I’ve followed the instructions from Google but the drop down menus for the Domain that it said were accessible via Wordpress aren't showing up so I need some help navigating this.

If I can find someone who is also able to look at Moosend and help understand why we're suddenly experiencing these issues that would be massively helpful. Thank you.