https://wordpress.org/plugins/regenerate-thumbnails-advanced/
For custom image sizes, use the 'snippet' plugin and code from
This is a nice plugin from makers of ShortPixel, which along with their other two image management plugins make a good 3 plugin combo.
https://wordpress.org/plugins/resize-image-after-upload/
https://wordpress.org/plugins/enable-media-replace/
Ideal when we need to update an image with the same filename.
https://wordpress.org/plugins/shortpixel-image-optimiser/
Free 100 credits monthly for simple set and forget.
regenerate-thumbnails-advanced