where is spark plug on my Honda Izy and how to clean/change it?

I put in wrong fuel - diesel and realised straight away as it stopped working so drained off immediately and replaced with unleaded but it still wont start. Have read up that I may need to clean the spark plug by taking out and washing, drying out and replacing it. I've never had a mower before so dont know how to do this or even where to find it or if I will need any tools to do this. Can anyone advise me on this? Thanks