To thoroughly delete an iOS app, including all settings, service workers, and data, start by deleting the app from your home screen. Tap and hold the app icon until it jiggles, then tap the minus sign in the corner of the icon to remove it. This action deletes the app but may not remove all associated data.

Next, go to the Settings app and select General, then iPhone Storage. Find the app you just deleted in the list and tap on it. You will see an option to Delete Data; tap on this to remove any data associated with the app. This step removes documents, data, or other files stored by the app.

Some apps may still have residual data or settings stored in other locations. To remove these, go to the Settings app and select the app's name, if it is listed. If the app has any settings or configurations, you can reset them or delete them from here.

Additionally, you can use the Offload Unused Apps feature in the Settings app to remove any unused apps and their associated data. To do this, go to the Settings app, select General, then iPhone Storage, and tap on Offload Unused Apps.

It's also important to check iCloud settings, as some apps may use iCloud to store data. Go to the iCloud website and delete any associated data from there. You can do this by signing in to your iCloud account, selecting the app's data, and clicking on the delete button.

For a more thorough removal, consider restarting your device to clear any temporary files or processes related to the app. This ensures that all residual data is removed from memory.

For maximum security and data removal, a factory reset of your iPhone is the most comprehensive option. Back up your device first, then go to Settings > General > Transfer or Reset iPhone > Erase All Content and Settings. This removes everything and returns your iPhone to its factory state.