While indexing, how do you "Control B" a space on a tablet? Thanks
You will need to use the toolbar icon to mark a Field BLANK:
The next tool marks the entire record (All Fields) BLANK.
The question mark tool marks the Field UNREADABLE.
If you have an Apple tablet (iPad) with an Apple-compatible Bluetooth connected, then the Mac version of the keyboard shortcuts will work. In your case that would be Command B. Otherwise you need to use the equivalent toolbar icons as @genthusiast has suggested.