Authenticator pops up on my iPhone even though it doesn't work anymore

Whenever I try to log into a website on my browser on my iPhone, Authenticator pops up and offers to fill in a username and password. Two problems: it doesn't actually work anymore, so I don't need or want it to pop up, and, most of the passwords it offers are ancient and defunct, for people who left our company 6 years ago or even longer. How do I delete those, and also, how do I get it to stop popping up at all?