how to switch sandbox account in iOS device

Now I am login apple using a new sandbox account, when I am using in app purchase. It still using the old account. I have tried: * close the app and reopen it and do in app purchase, but still popup UI using the old sandbox account * reinstall the app and do in app purchase, but still using the old sandbox account * tried in another ios device(iPhone XR) using the new sandbox account(the app still using the old official app id) what should I do to switch to the new sandbox account? By the way, I am using iPad, and the software version: 14.6.