java - How to add values to Firebase Firestore without overwriting?

Question

I have two Activities, I am adding data to Firestore from these two activities individually. But, whenever I add second activity data to Firestore, it is overwriting the first activity data. I used below code in the two activities:

 firebaseFirestore.collection("Users").document(user_id).set(data)

How to stop overwriting? I want to save both Activities data in the same user_id.

Answer 1

Waitting for answers