Hi Robbie,
A surface is automatically closing an app after they have not been used for awhile.but there are some reasons you might want to manually go back in and close them yourself. To do so, you may follow the steps below:
Method 1: Dragging the app window down from the top of the screen
• In tablet mode, apps run fullscreen so you don't get the "X" in the top right-hand corner you might usually use to close it. To do it, simply drag your finger from the top of the screen down to the bottom. Halfway the app window will shrink right down, just keep dragging until an animation pulls it off the bottom of the screen.
Method 2: Through Task Manager
• Firstly, you'll need to open up the Windows Task Manager by pressing CTRL + ALT + DELETE. From there, simply find your unresponsive program, right-click and select Go To Progress (not End Task). The Processes tab will open and your program should be highlighted. Now, press the End Process button and select Yes.
Let us know if the above resolution answers your query.