re: the preview panel has some other page displayed when I needed to make the change for the single view.
What do you mean by this??? When you access the Template Customizer you should be taken to your directory home page which has a preview of the template being customized.
If you are not, make sure that you have correctly set the Directory Home Page option on the Connections : Settings admin page under the General tab. This page must be a public page and not a draft or preview.
re: I think I need to learn how to access the Connections template while the correct page is still showing in the preview.
You can access the single entry preview from the preview page by clicking an entry name… their name links to the single entry view which then can be customized. It does not matter which entry name you click on to get to this view.
Hope that helps!