My debugger pane got displaced accidentally

I clicked somewhere in PyCharm and suddenly the debugger pane went out of the original place, meaning that it is not placed in the lower section of window any more, but was placed in  a separate window. Whenever I debug a file, the debugger window pops up and the position of the debugger isn't good. I can't let the debugger pane to back to its original place. I don't want to reinstall PyCharm.

How can I get the debugger pane back to its original place?