I don't know how to cancel my free trial please help me

Here's a link on how you can cancel your subscription https://support.apple.com/en-ph/HT202039

Go to your settings go to your Apple ID then click iTunes&App Store after that click the Apple ID and then it shows options click the one on top that says View Apple ID and then end the subcription you want to end. Hope this helps and sorry about my bad english.