On the monitor itself there should be some button which allows you to access its controls - menu or something like that. Find the "degauss" function and operate that. It may not work the first time - or even subsequent times if its really distorted. Don't do it too much as it can wreck the monitor - but you may have done that already.
If it doesn't work it's hands deep in pocket time and remember to be more careful with your next one!