Simple App is an app that does not require membership or account registration. Therefore, there is no procedure for "cancellation."
There is no risk of unexpected charges, nor does the app send any entered data to the server. You can leave the app installed in case you need it in the future without any concerns.
However, if you still wish to delete the app, please remove it from your home screen.
We are sorry to see you go, but we are very glad that you used our app. We hope you will think of us again if you need it in the future. Thank you very much for using our app.