It's not very clear what you're wanting to happen here. But if you are using the same attribute on both screens then of course it will show the same value.
If you want it to show different values then you will need to assign different attributes and have the mapping handle the difference (ie the integration layer will need to handle that when user 1 starts that it sets the value for "the user 1 identity" and then when user 2 starts it will set the value for the completely other attribute "the user 2 identity").
If you want OPA to show 2 different things then you will need to give OPA 2 different things to show. Remember that OPA is stateless - something else needs to "remember" that you had user 1 here last time.