IBM 3270 Manual page 113

Now, let's move the second window to the upper
right corner of the screen:
1. Press the Right Cursor key.
The window moves to the right.
2. Keep pressing the Right Cursor key until the
window has moved to the right side of the
screen.
You could also press the Corner key (PF10) to
move the second window.
If you do you will
have to move it down and to the left to see
the whole border.
9-16 Book 3 - Using the Control Program