Here's how to merge the two release groups:
(I haven't done it so you can do it)
After you've entered the edit to merge them, you will have to wait a week for the edit to go through.
This is to give others time to have a look at your edit and leave notes and check for mistakes (teamwork!)
You can see open edits by clicking 'open edits' on an artist/release/editor/recording page, which will give you something like:
I see you've merged all the releases here:
Which I assume is by accident? Left a note there as well.
Hope that helps!
Any other questions just ask, thanks for your edits