When I open the modify header extension, it opens outside the monitor and I can only press the "OK" button; In other word I cannot see the button that are in the upper part of the pop-up.
If you are referring to Modify Header by Gareth Hunt, its window is resizable. I tested it in Windows 10. So, do either of the following:
- Press Windows+Right or Windows+Left to force it snap to either the left or right side of the screen.
- Press Alt+Space to open its system menu. Then use Resize command and keyboard to resize it to fit in your screen.