For almost all installed add-ons on your website you have settings for each of them. You can simply access it via the listing by click on the gear:
By clicking on it the card will flip over and then all the settings will appear:
The custom views allows you to override the way AcyMailing insert content in the editor. To edit it you have to go in the settings of an add-ons which insert content and then simply click on the button Edit custom view. A modal with a HTML editor will open:
As you can see the modal is separated in two parts:
On the left you have the editor which is the custom view
On the right you have all content that you can insert for this add-ons
If you open this modal for the first time we displays a simple structure so you not have to start over.
To add a tag you simply have to click on the one you want in the listing, this will insert the tag were your cursor is in the editor.