Student Marks Apps using Flutter and Firestore

I'm looking to develop a app to store student marks.
And I'm using firestore database to store that data.

I created two collections student_info and subject_info
In student_info collection there are 5 student documents and they have 3 fields student_id, name, active_status and in subject_info collection there are 3 subject documents and they have 2 fields subject_id, subject.

How do I connect these two and add their marks?
I'm using flutter.
Thank you!