Specify user for idp initiated sso

I have 2 applications in auth0 which have been configured for sso.

application2 has saml2 addon enabled, and the user can log in using idp initiated sso.
It can also be accessed using sp initiated sso.

Now App1 (ReactJS) has the link for App2 which the user will click on and gets redirected to app2. I have configured the SAML assertion and other stuff but I am unable to figure how to specify the user which has to be logged in while getting redirected to the app2 from app1. Something like login_hint?