The notes window appearing as the bottom half of the translation page can be re-sized or closed using the buttons in the separator bar between the Gemara and notes.
There is an "X" at the right end of the separator bar that removes the notes window and displays Gemara over the full page. You may have tapped it by mistake. The easiest way to reopen the notes window is to tap on a footnote number in the Gemara text. That should reset the notes window to show you the note you selected.
The notes settings can be fully configured in settings (the gear on the top right) under the the Footnote Settings section. See Notes Settings
for more information.