I can’t see any way to customize the Google Authenticator (i.e. TOTP) prompt page that the user sees. The example code says there is an “issuer” field where you can supply text to the user, but it’s not displayed.
the label shown in the authenticator app
Customize Multi-Factor Authentication Pages
This is a real problem in a system with several apps - the user could do with reminding which code in Google Authenticator to use.