Before a track day, become familiar with the recording controls in your installed app version while stationary. Give your session a recognisable name if that option is available and check how you will find it afterwards.
Make a short recording first and confirm that the result is what you expect. Note the app version and equipment used so later questions have useful context.
Complete phone setup before driving and follow the organiser's rules for devices and mounting. This guide does not assume a particular sensor, connection or recording mode.