There are two ways to choose IDP:
1. Once the multiple IDPs are configured in the plugin. The drop-down list appears on the login page at the time of SSO. This list contains name of all the configured IDPs. You can select your IdP from the list and enter credentials for the same to perform login.
2. When more than one IDPs are configured in the plugin, Domain Mapping option enables. Using this option you can set domain of the IDP you want to perform Signle Sign-On with. At the same time you can configure more than one IDP domain also. It will redirect to the IDP based on the domain name you entered for the login.
Suppose you configured okta and azure domains in the domain mapping fields.
Domain mapping : okta.com
Domain Mapping : azure.com
On SSO it will ask to enter the username. If your username contains okta(okta.com) domain it will redirect to okta idp and you need to add username and password for the same IDP to perform sso.