Moving folders - already exists - How To Merge?

After importing from a couple different devices I ended up with at least two folder structures divided up by shot date. I'd like to combine them into a single date organized hierarchy. There are dozens, maybe hundreds of folders in each hierarchy. The unique folders move OK, but they aren't all unique (same date from different devices) - when I try to move those folders I get this:

How do I get Lightroom to MERGE the folders that already exist?