How to remove a third party iPhone app and download a fresh copy

I have been using an app (WW) for a long time and I believe something has gotten corrupted as it no longer works as it should. I'm not sure how long ago this happened, but I have tried deleting the app and turning off the phone several times. When I download the app again, I get the same problems. I have also cleared the cache various times on the iPhone 13 Pro X. I'd like to know if there is something else I need to do to clear out any remnants of that app before trying to reinstall it. Any help would be appreciated.