Redirection (plugin) help setting up

Can anyone help me set up the plugin redirection?

I moved all my image galleries to a new sub domain galleries.robbmccormick.com from www to be able to create a wordpress site on my main www.

All the links are the same, the only difference being http://www.robbmccormick.com is now galleries.robbmccormick.com.

I have installed the redirection plugin but can’t seem to figure out how to set it up. I need to set it up so 404’s get just fowarded over to the new sub-domain and keeping the rest of the URL the same.

Example:

Old: http://www.robbmccormick.com/2016/image.jpg
New redirect: http://galleries.robbmccormick.com/2016/image.jpg

Is there a way to automatically forward the 404’s to the sub gallery? I have 50,000 404’s in Console and it’s way too many to do manually.

I’m ranked page 1 and 2 of google and afraid I may lose rankings with all the dead links to galleries and images.

Any help setting up redirection to match the above would be helpful!

Thanks!!!