Hi John
Not sure what you mean.
When on the WEB UI select the artist you want to add art to, on the right hand side you will see all the albums by that artist, click on the three dots to the right of the album you want to find art for and select Get art from either musicbrainz or amazon, click on the one you want to use.
If you do have some very obscure albums you may not find anything but both are currently working.