From the main file browser (from the upper left menu button in the editor), find Python Modules. Then under that you should see site-packages, or site-packages-3. Under one of those you will find a stash folder, also anything you have installed with pip. Just delete the stash folder and anything you thing was installed by mistake, or was installed by pip. You can use the edit menu to select a folder then trash it.

You might be able to just rerun the install script, after doing a force quit.