We vividly suggest reusing any box you might already have lying around: a cereals box, a shoe box... anything goes.
Place your device inside - remember to be careful, as old electric shaver heads / blades can still be quite sharp.
Make sure all items are dry.
Find old paper/newspaper/bubble wrap/bags.
Wrap the item(s) up, fully covering them.
Place them in a box, ensuring everything is tightly packed, so they don't move on their way.
Remember to be careful at all times!
Then seal the box and add the shipping label. You should be good to go.