Breathe in when the timer is counting up, breathe out as it counts down. Breathing slowly is calming. Can you rather visualise the timer so that you breathe in when the circle gets bigger, and breathe out when it gets smaller. You can do this by making the circle get bigger as the timer counts up, and then get smaller as the timer counts down. (You can then hide the timer)
I got the images from https://www.hiclipart.com/ I was inspired to make this by Natalie's project --> https://scratch.mit.edu/projects/1320558/