Sorry to hijack here, but I have a very similar problem, in that I had a bunch of installations in my Mamp 5.2 and upgraded to Mamp 7.1. I didn't know that I had to export dbases like you describe and thought by just copying my htdocs file to the new Mamp App folder, it would be ok, (call me ignorant). So now, I have the new phpmyAdmin, sitting there empty, and I can't access my old installations.
Is there a 'safe' way of doing this? I'm a bit clueless when it comes to db handling, other than just creating a db and a new user.
Thanks in advance!!!