I've seen answers to this topic already and tried the solutions, but it seems that when I updated the NextGen gallery this past week, the settings were lost.
Now in my Yoast SEO the area in the set-up, under Taxonomies, there is not a place to set the template for "Ngg_tag". It was there before the update and now it's gone. My images were in Google images and I'm afraid that they will be lost or that new images will not get into Google Images.
Now when I go to Webmaster Tools it's showing that my images as errors and the Next Gen gallery is not in my sitemap.
Thank you for your help.