The Relay Plus drill is an extension of the outfield relay.
You can think of it as the double-cut except you will have them go back up the line of kids.
You take four kids and space them out in one line. They need to be far enough to throw to each other.
Then they just throw it to each other down the line and back.
Here’s an image that might help.
Depending on the age group, you will need to space the kids out a little more.