Go into appearance-editor and add the following to each CSS page title item:
visibility: none;
you can also try:
height: 0px;
Also make sure you don’t have any page title items with padding. If you do change them, for example change this:
padding: 40px 0;
to this:
padding: 0px 0;
Also if your theme has a Design – Custom CSS (or similar) option in the “Customize” section you can simply add this there, which is the preferred way to do it since updates to your theme can overwrite any code changes you make to the CSS files, but the tuff you put inot the custom CSS will stay in tact.
FYI … In my opinion hiding this is something every theme should provide a toggle, but I don’t know of any that do. Maybe customizr does … not sure.