Press the soil firmly around the plant. Shape the soil to the bowl of the plant collar (see the picture). It is important that the funnel shape lies horizontally.
Before you place the plant collar around the plant, the small breathing holes in the collar have to be made free.
Now you can place the collar around the plant. You have to ensure that the lock mechanism is kept locked or else the collar will reopen.
Then you fill up the collar with soil until it levels with the ground and you cannot see the plant collar any more.