You can Select All in each tab.
1. Go to the file tab in which you want to select all files
2. Click to 
more button at the top right of each tab and then Click 'Select all'.
How do I select all files?
You can Select All in each tab.
1. Go to the file tab in which you want to select all files
2. Click to more button at the top right of each tab and then Click 'Select all'.