AppleCare plan I need to change because the store gave me the wrong one I have the basic not lost n left

I just bought AppleCare for an iPhone 11 I was supposed to get the AppleCare lost and theft how do I go about changing this I just purchased this today and Saturday is the last day to get the Apple care I don’t know if they can change it from one plan to another without canceling or I have to cancel and re-purchase because I know you have 30 days to cancel please help how do I change my Apple care plan on my iPhone 11? And also they charge me to pay monthly instead up for the front and my phones only 4G phone so I don’t know if it’s worth having the AppleCare lost and thft for more than 24 months