I'm using MP3Tag via Wine for MacOS, and no I cannot upgrade at this time... Blame Apple Music for that.
I accidentally clicked the X (I think) and even in the drop down menu from View, I can't find how to put it back there.
Thanks.
It's called "Tag-Panel".
Ctrl-Q should get it back.
If the tag panel has become undocked, perhaps this thread helps:
Did you follow the description in the linked thread?
I can't reply to that topic now so it's no solution to me. How do I restore MP3Tag to it's original state? I did a reinstall, it's the same.
close MP3tag and delete mp3tag.cfg
Then start MP3tag again.
No such file exists.
I found this thread:
I don't use a Mac or Wine or anything. So I cannot offer any further help than the search.
So, I think that you can use the search function yourself from now on.
Linked thread is locked so I can't comment further to tell them how unsolved it is.
I thought that you wanted to get the tag panel back into position.
So: which steps did you try, what did you observe additionally to "did not work"?
I ended up wiping MacOS and installing Linux! 
Unfortunately the MP3Tag equivalent 'Puddletag' isn't nearly as good as this one though. Respect to all who made it possible.
Thanks for your replies.
In Crossover (special flavour of Wine), it is in:
/Users/%username%/Library/Application Support/CrossOver/Bottles/%bottlename%/drive_c/users/crossover/AppData/Roaming
It should give general idea. just replace "Crossover" with "Wine" in the path.
But I do have a question, why did you not use native version in MacOS?
On Linux, I would sue Mp3Tag via Wine, PuddleTag does work, but it lacks lot of refinement, Mp3Tag has, it is much younger software too.
In this case, it should be further down the path:
drive_c/users/%username%/AppData/Roaming
The function
File>Open configuration folder
should get you to the configuration folder.
Otherwise, the installation folder is a good address.