Adjust the strap to ensure a snug but comfortable fit
To adjust the strap size, change the position of the popper before putting doppel on. Choose the hole you want for a snug but comfortable fit, then push the strap down hard over the round top of the popper.
To make sure the popper is secure, push the strap around the popper edge, and check the strap is flat. You can change the position as many times as you need.
And don’t worry, there is a spare popper in the box if you lose the first one.