Continue writing the next sentence in this paragraph:

How to send a message forward in time
Get the needed supplies listed under " things you'll need ".
Write a letter to yourself as if you were someone else.
( i.e. use " you " instead of " i " )
Write down anything you'd like yourself in the future to remember, or just give your future self some encouragement.
Who knows, maybe you'll need it one day. Write the letter in any format you want to write it in, it doesn't have to be formal.