How to cancel the pulse checker app?

Managing auto-renewing subscriptions -

http://support.apple.com/kb/HT4098

M1 Mac mini, macOS 11.2.3; Watch, series 5 GPS/cellular, watchOS 7.3.2; iPad Pro 2nd Gen, iPadOS 14.4.1; iPad Air 2, iPadOS 14.4.1; iPhone 12 Pro, iOS 14.4.1; TV 4th Gen, tvOS 14.;  HomePods, audioOS 14.4.1 and Airport Express w/ Airplay 2

Hey lady, Apple is not here. This is a volunteer forum of folks who use Apple products. NO ONE here has access to your account for you to order us around to cancel this for you.

I gave you a link above on how to manage subscriptions. THAT is how you cancel a subscription, NOT in an app and NOT by deleting an app and NOT by making a stop payment at your bank.

If you have your bank stop payment because at 85 you haven't figured things out, you will also cause Apple to freeze your account and you won't be able to use it at all. You won't be able to buy anything, you won't be able to download anything that is free and you won't be able to update anything you already have.

So, click the link that I gave you above and read about subscriptions. Or have someone else read about it and explain it to you.