This document defines some errors you may see while creating connections in Flow or Power Apps, and provides some troubleshooting steps and possible solutions.
User is unable to Switch Accounts on a Connection
The behavior in this scenario is that a user tries to switch the account for an OAuth connection that they have created. However, when the pop-up is displayed and the user enters their credentials, they are simply redirected back and see that the account information for the connection hasn't actually updated.
A possible reason you might see this issue is because of Single Sign-On Policies in your Azure Active Directory (AAD) tenant. If single sign-on is enabled, your browser may prevent the currently signed in user to be logged out and instead tries to keep the user signed in.
One way to work around this is to open up another browser or incognito window, sign in as the user that owns/has access to the connection, and try to switch accounts on the intended connection. This should update the connection name and account details for the connection.