I’m interested as to how you managed that in the first place.
Are you able to drag the window? If so, have you tried dragging it into the top, bottom, left or right of your Roblox Studio application? Usually it will snap to the side if you drag the window near enough.
It may also not be your fault and could be a Roblox Studio glitch, although I’ve not seen it before. Did this start happening out of the blue or do you think you did something to make this happen? I recommend you try restarting your PC and reinstalling Studio if you haven’t already, if the problem keeps persisting. Haven’t seen this issue before so I’m not too sure what to do about it.
Did you try a reinstall of Roblox Studio? If all of these things don’t work, I recommend you make a Studio Bug report in the Platform Feedback category.