Google Smart Lock is very useful to some extent. But if something goes wrong with it, it becomes worse. This happens to everyone when you change the password of Facebook or Instagram but GSL uses the old password for single click login. If you do not like GSL at all and you do not want to use it anymore, then you can directly remove Google Smart Lock from the app in your phone instead of changing the password. If you want to continue using GSL on your phone, just change the saved password on Google Smart Lock and keep using it without interruption.
How to change the saved password of an app on Google Smart Lock?
If you try to find the option to change the password on Google Smart Lock in the Settings of your phone, you will not find it anywhere there, because it is not present in the Settings but in the Google Account Manager.