Prepare the worksheet attached. Print it side to side.
Get the students form a circle with their desk. If the space isn't enough, you can have inner and outer circle.
Give students the worksheet, let them write their names in the middle box. Then tell them to fold the paper in three (use the guide lines)
Play a song of your reference while students pass the paper (having the letter envelope drawing face upward) clockwise. When the music is paused, students check the name/owner of the paper they are holding and write a letter for that student. Give them 5 minutes (depends on your class' pace) to write a message. You may let them use their textbook for reference or show them message examples: You are ~. Don't give up. You are a great =. I like your~. Let's~. Please do your best next school year.
Do it 5 times to fill out all the message boxes.After all message boxes are filled out, let them give the letter they are holding to the owner.
Variation: You may ask students to write their codenames in the signature part. You may confirm this to your JTE. My JTE personally preferred students write their names instead of a codename.