Subject and observer changes to be seen by both in Kotlin

How can text entered by subject and observer on their individual screens(ie same activity on diff screens)be visible to both in a recyclerview in activity.

For eg:User 1 enters apple and user2 enters mango so the activity should show apple,mango.Then User 1 enters bat and user2 enters ball,so the activity should now show apple,mango,bat,ball.

I know how to create recyclerview but is there a way to get all changes made by sub n observer.

Can this be done using observer pattern in kotlin?

Please provide some useful link or logical information or which design pattern or method to use.