Please follow these steps to change your Google account for in-app purchases:

1. Add the account you need to your device (Settings -> Google -> Account -> Add account)
2. Delete the app.
3. Go to the browser version of the Google Play store.
4. Check the Account tab in the Google Play menu to make sure you've logged into the right Google account.
5. Find the app and install it.
6. Open the app and try making the purchase again.

You can also read this article on how to add Google accounts to your device.